[8.0] Postscript: The Other Shuttles

v1.1.0 / chapter 8 of 8 / 01 feb 15 / greg goebel / public domain

* The US space shuttle was by no means the end-all of work on reusable launch vehicles. The Soviets built their own counterpart, named "Buran", and flew it once, but it never became operational. Other work on reusable launch vehicles and spaceplanes also took place, and continues in the 21st century.

ESA Hermes

[8.3] DC-X / X-33 / X-34
[8.4] HL-20 / X-38 / X-37 / DREAMCHASER


* The Soviets had watched the emergence of the US space shuttle program with discomfort, not merely because the shuttle seemed to be focused on American military dominance in space, but because it also seemed to be evidence that the Americans were getting ahead of the USSR again. In June 1974, the word came down from the Kremlin to the NPO Energia space-systems development organization to build a Soviet shuttle -- the "Reusable Space System" or "MKS" in its Russian acronym -- as soon as possible. The project was driven heavily by the Soviet military, which wanted a heavy-lift vehicle to launch large military space assets.

Various options were considered, with the minimum solution a spaceplane launched by a Proton booster, the maximum solution a lifting body twice the size of the US shuttle, and the middle-of-road solution a design based on the US shuttle. The middle-of-the-road solution was chosen in early 1976.

However, the result was by no means an outright copy of the NASA shuttle. Although the MKS used an orbiter named "Buran (Snowstorm)" that was easily confused with the NASA shuttle orbiter, there were fundamental differences in design philosophy. The most important was that while Buran had an orbital propulsion system, designated the "ODS", comparable to that of the NASA shuttle orbiter's OMS, the Soviet orbiter did not have main engines. Buran was to be launched in a piggyback fashion on a large expendable booster -- the booster being named "Energia" late in the development program, after the design bureau.

The Energia booster featured a large core stage and four liquid-fuel strapon boosters. The expendable booster configuration was chosen because Valentin Glushko, the boss of NPO Energia, believed that his bureau could develop an expendable engine that approximated the capabilities of the NASA shuttle's SSME within the given schedule, but building a reusable engine with such capabilities was not feasible. Since the engines were not reusable, that meant that there was no reason to put the engines in the Buran orbiter and no great reason to try to recover the external booster. Liquid-fuel strapons were to be used since the USSR lagged the US in large solid rocket engines; besides, Soviet rocket designers felt comfortable with liquid-fuel rockets, were very experienced with their design, and found them perfectly effective.

The core booster in the Energia vehicle was to be powered by the USSR's first operational LOX-LH2 engine, the "RD-0120", providing 2,256 kN (230,000 kgp / 507,150 lbf) thrust. The two strapon boosters were to be powered by the "RD-170" engine, then under development, with four chambers and a total of 7,906 kN (806,000 kgp / 1,777,000 lbf) thrust. The RD-170 was to use LOX-kerosene propellants. In principle, the strapons were to be recovered by parachute and reused up to ten times.

The Soviet MKS would be much less reusable than the American shuttle -- though given the history of the NASA shuttle, a case might be made that the Soviets came out ahead with the less ambitious route. However, the MKS would have a greater payload capability, up to 30 tonnes (33 tons), and as an unambiguous plus, the Energia booster could also be launched with an expendable payload module in place of the Buran orbiter. That would give the Soviet Union both a shuttle and a heavy-lift booster, matching the American shuttle while making up for the unhappy N-1 Moon rocket program of the 1960s, which never performed a successful flight.

The Energia booster was to be designed in a modular fashion, allowing it to be used to launch lighter payloads if only fitted with two strapons and heavier payloads if fitted with six. Some of the subsystems on the Buran orbiter, such as the docking adapter, airlock, and robot arm were also to be designed in a modular fashion for re-use on other space projects.

* The initial schedule envisioned first launch of the Energia booster in 1983 with a dummy orbiter payload, leading to first launch of a crewed Buran orbiter in 1987, the seventieth anniversary of the Russian Revolution. Given the ambitious nature of the project it was not surprising that it soon began to slip behind schedule. The RD-170 engines for the strapons proved troublesome, as did simple manufacturing and systems integration of such a complicated system. However, Glushko and his political patrons pushed the program forward. Mockups were implemented, and work progressed on the extensive ground facilities needed to support the MKS.

Three Myasishchev M-4 "Bison" bombers, roughly equivalent to the US Boeing B-52 if not as successful, were converted to carry bulky payloads on their backs from industrial facilities in the Moscow area to the launch facility at Baikonur in Kazakhstan, with a precision straddling crane set up at each end to handle the payloads. The converted bombers were given the designation "VM-T Atlant"; they featured oversized twin tailfins, required to maintain control when a big payload was being carried piggyback.

The VM-Ts were used to carry fuel tanks and other large assemblies. They didn't have the lift capacity to carry a fully-fitted Buran orbiter, so the Antonov aircraft design bureau began work on a Soviet counterpart to the NASA Boeing 747 SCA, derived from the An-124 "Condor" heavy cargolift transport. The new machine, the "An-225 Cossack", was to have six oversized turbofan engines, big twin tailfins, and would be the biggest aircraft ever built. The Soviets would produce two, with the first flying in 1988.

The Soviets also modified two Tupolev Tu-154 jetliners to evaluate Buran flight systems and to help train Buran crews, providing an equivalent to the NASA Gulfstream II STA shuttle trainers. A new spacesuit, named "Strizh (Arrow)", was developed as well, being a "rescue suit" along the lines of the shuttle ACES suit. All in all, there was just too much to do, and by January 1986, the schedule had fallen so far behind that it was coming down to a choice between getting really serious or giving up. The decision was made to get serious, and the program put on highest priority.

* At that time, the Americans were struggling to return to space, while the USSR had flown a modular space station, "Salyut 7", and was keeping it in near-continuous operation. As if to emphasize Soviet superiority, an all-up flight test of the Energia booster was conducted on 11 May 1987 with a military payload, an experimental space "battle station" named "Polyus (Pole)", built in response to the American Star Wars effort. The booster worked as specified, though the payload suffered a guidance system failure and didn't make orbit. Still, the USSR had launched a payload weighing 100 tonnes (110 tons), breaking the Saturn V's launch record.

shuttle versus Buran

That was followed by a launch of the full MKS shuttle system with an automated Buran orbiter on 15 November 1988. The Buran launch was actually four years behind schedule, but of course that wasn't mentioned in Soviet press announcements. The entire flight lasted about three and a half hours and was automated from launch to landing, an impressive feat. Many of the cosmonauts had pushed for the first launch to be crewed, but that was ruled out, the system being judged inadequately debugged.

The chant of "the Reds are ahead" made a resurgence in the USA after a lapse of about two decades. Berk Breathed's popular Reagan-era comic strip BLOOM COUNTY expressed the frustration of American space enthusiasts when one of the strip's characters, boy genius Oliver Wendell Jones, fumed: "The indignity of being beaten in space ... by a country that can't build a decent ... TRANSISTOR RADIO!"

The sense of being behind didn't last long. Within a year, the Soviet Union was falling apart. Buran and Energia never flew again; the orbiter was destroyed when its hangar collapsed in 2002. A nonflying test article of the orbiter survives as an attraction at Gorky Park in Moscow.



* While the US struggled to keep the shuttle operational, the US and other nations were investigating next-generation replacements, though with dismally poor results. In 1985, US President Ronald Reagan announced that the US would commit to development of a hypersonic spaceplane that could fly to orbit like an aircraft. Reagan referred to it as the "Orient Express", though, in reality, this was confusing the spaceplane with proposals to build a new supersonic transport airliner. In any case, it was another example of Reagan's fondness for grand technology projects of questionable credibility.

The project emerged as the "X-30 National Aero-Space Plane (NASP)", a joint program run by NASA and the Department of Defense. The original objective was to build two prototypes, with an estimated cost of $3 billion USD and an initial flight in 1993. NASP was to be a reusable launch vehicle, envisioned as a wedge-shaped aircraft that would permit "single-stage to orbit (SSTO)" flight. It was to be powered by "supersonic combustion ramjets (scramjets)" to the edge of space, where rocket propulsion would take over.

A conventional ramjet engine is just a "stovepipe", a tube contoured to provide some compression of the inlet flow, along with a fuel injector system and an igniter to burn the fuel. Combustion takes place in a subsonic airflow, though it is useful in this context to realize that the speed of sound is several times higher in a high-pressure, high-temperature airflow. To reach higher speeds, it is necessary to support combustion in a supersonic airflow, which is difficult to do in an engine of any reasonable length -- a trick compared to lighting a match in a hurricane, and keeping it lit.

Building a scramjet is tricky, and nobody built one to the end of the 20th century that amounted to anything more than a preliminary test system. The other major obstacle to NASP was to find materials that could tolerate high temperatures, have light weight, and still remain within the limits of reasonable expense. Analyses showed that the NASP would need an empty weight only 20% of its fully loaded weight; even optimized high-speed aircraft like the Lockheed SR-71 Blackbird reconnaissance aircraft had an empty weight more than 30% of fully loaded weight.

NASP wind-tunnel model

Critics began to poke fun at the program, claiming the engineers were after "unobtainium" -- a remarkable substance whose weight converged towards zero while thermal resistance, strength, and cost rose toward infinity. Of course, the project began to fall behind schedule while the pricetag climbed, and the military began to look for an exit. In 1993, the program got the axe, though work did continue on small rocket-launched scramjet demonstrator vehicles. Of course, once the Americans had committed to NASP, the Soviets had to follow, or try to follow, beginning a program in 1986 to build the "Tupolev 2000" SSTO launch vehicle. Since the American effort was basically hopeless, the Soviet effort was effectively dead at the outset.

* In the meantime, the ESA was considering jumping on the shuttle bandwagon, if on a relatively modest scale, in the form of the "Hermes" spaceplane. Hermes was a somewhat larger and more sophisticated take on the old X-20 Dyna-Soar concept, with a winged piloted spaceplane launched on an expendable booster, in this case the Ariane 5 heavy-lift booster. Hermes had evolved through the early 1980s in parallel with the Ariane 5, and was originally a purely French project. However, costs were obviously going to be significant, and so the French pushed Hermes as an ESA project, with the Germans coming on board as the program's major financial partner. Aerospatiale of France was awarded the initial development contract in 1985.

As Hermes emerged, it had a general resemblance to the Dyna-Soar but with more rounded lines. It was also bigger, with accommodations for three "spationauts", as the French called them; a pressurized payload bay; and an expendable pressurized supply module attached to the base of the spaceplane. It was to be capable of extended stand-alone orbital flights of up to 90 days. It was also intended to support the "Columbus Man-Tended Free Flier (MTFF)", which was a small space station that would be visited periodically, to be loaded up with experiments that would be then conducted unattended. The ESA also collaborated with the Soviets to develop a spacesuit for Hermes, the "European Space Suit System (ESSS)", later the "EVA SUIT 2000", based on Soviet designs.

The loss of shuttle Challenger had a strong negative impact on the Hermes program, since the goals of the development program had to be modified to provide increased crew safety. Crew escape capsules were considered, but finally ejection seats were specified. Even this compounded the tendency, all too common in leading-edge aerospace programs, toward weight and cost creep. The weight creep kept eating into the spaceplane's payload capacity. By the end of the decade the Hermes program was on increasingly shaky ground, and it was axed in 1992 without prototype being built. The EVA SUIT 2000 program was canceled as well, though Columbus would survive as a module for the ISS.

* The British were also working on an automated SSTO RLV named HOTOL, for "horizontal takeoff and landing". HOTOL was to take off of conventional runways using a rocket-powered wheeled trolley. It was to be powered by "combined cycle" engines built by Rolls-Royce, which operated as air-breathing jets in the atmosphere and pure rocket engines at high altitude and in space. Interestingly, HOTOL was to be basically an automated vehicle, though it could be fitted with a crew module if required for a mission.

Studies for HOTOL were begun by a group of engineers at British Aerospace and Rolls-Royce in 1982. The British government provided funds for investigation for a few years, but as the HOTOL design effort progressed, it became increasingly clear that it could carry a useful payload only if it were built of unobtainium -- it seems this is a common characteristic of SSTO RLVs. Britain, unlike France, had never been very space-happy and funds were soon cut, the program being axed in 1988.

West Germany was also studying a more conservative two-stage RLV named "Saenger II", with "Saenger I" having been Eugen Saenger's World War II antipodal bomber concept. Saenger II was to consist of a delta-shaped hypersonic launch aircraft carrying a rocket-propelled spaceplane, along the lines of the Dyna-Soar or Hermes, on its back. The launch aircraft was designed to be adaptable as a supersonic transport.

Saenger II was a paper project and never amounted to any more than that, though it lingered on into the early 1990s. The simple truth was that getting into space was hard. There had been tremendous advances in propulsion and space systems technology in the 1950s and 1960s, but then diminishing returns set in. After that, trying to take a giant step forward almost always turned out to cost more than could be justified by estimates of the potential return. Figuring out a more incremental approach that could be sold to the politicians was difficult.


[8.3] DC-X / X-33 / X-34

* In parallel with developments such as Pegasus, the US continued to work on the elusive goal of the RLV. In parallel with the dead-end NASP effort, the Strategic Defense Initiative Organization had been interested in building an SSTO RLV to put SDIO payloads into orbit. After a sequence of studies and proposals, in August 1991 the SDIO awarded McDonnell Douglas a contract to build the "Delta Clipper Experimental (DC-X)" demonstrator vehicle. The "Clipper" in the name called back to the Clipper flying boats of the 1930s and 1940s, which pioneered international commercial passenger travel, and the DC-X was seen as a stepping stone to technologies that could similarly open up space travel to a wider audience.

The DC-X was completed in an amazingly short time, performing its first flight on 18 August 1993. It was strictly a demonstration vehicle and was incapable of performing flights anywhere near the threshold of space. It was instead meant to demonstrate enabling technologies for an operational vehicle, and in particular was to show how a space vehicle could be operated in a fashion similar to that of a commercial airliner, with modest support needs and a quick turnaround.

The DC-X follow in the steps of McDonnell Douglas studies back in the late 1960s for vertical takeoff and landing SSTO vehicles, beginning with the "Rombus" concept and proceeding through a bewildering range of studies. The DC-X was unpiloted, being was a blunt, four-sided wedge about 12.2 meters (40 feet) tall. It launched and landed vertically on a set of four retractable landing legs, and was powered by four RL-10A5 LOX-LH2 engines, like those used on the Centaur upper stage. The Strategic Defense Initiative was pretty much dead by the time the first flight took place, and only three flights were conducted before the effort ran out of money.

Dan Goldin found the effort very interesting, however, and stepped in to rescue the program in January 1994. NASA went on to fund an improved and slightly larger version, the "DC-XA", also known as the "Clipper Graham", after Lieutenant General Daniel O. Graham, who had helped push through the original DC-X program. The DC-XA performed its first flight in the spring of 1996, but on 31 July 1996, on its fourth flight, it failed to extend a landing leg, tipped over, and exploded. There had been consideration of an operational derivative of the DC-X, the "DC-Y", but the loss of the DC-XA ended the program.

* By this time NASA had established a more formal RLV program that was pursuing two new experimental vehicles, the large "X-33" and the small "X-34".

The X-33 was to be an uncrewed SSTO RLV. In 1996, after an intense competition, Lockheed Martin won the award with a lifting body design that would take off vertically and land horizontally, and featured an unorthodox "aerospike" engine concept. The aerospike engine to be used by the X-33 would not have an external bell like that of a conventional rocket engine, instead simply having a central "spike", with the atmosphere providing thrust confinement. This in theory allowed efficient exhaust performance through the entire flight profile, in contrast to a fixed bell exhaust, which was optimized for only one segment of the flight.

X-33 / VentureStar / Shuttle

The X-33 was to be a demonstrator, not an operational vehicle. It was hopefully to be followed by a scaled-up full operational vehicle, which eventually emerged on paper as the Lockheed Martin "VentureStar". The NASA plan assumed that the commercial sector would bear a considerable portion of the development costs, in return for a guaranteed set of government payload launches.

There was skepticism over the X-33 from the outset. The X-33, as an SSTO RLV, ran into the same problem as other SSTO RLV concepts: its empty weight requirements dictated that it had to be made of unobtanium. Officials involved with the X-33 program also felt a need to be cautious about the prospects of building an operational follow-on vehicle, since they remembered the "voodoo economics" that were used to sell the shuttle and didn't want to make the same mistake again. That was one the motives to build the demonstrator: prove the idea and then take it from there. Had the shuttle program started off with a demonstrator, it might have gone a bit more smoothly.

* The X-34 program got off to a shaky start. Originally, it was defined as an air-launched booster like the Pegasus, though it was to be reusable and have a liquid-fuel engine. OSC and Rockwell International collaborated on the original proposal, but NASA was proposing that full development be heavily supported by company funds, and the financial analyses of the accountants on the OSC / Rockwell side showed that it wouldn't pay off.


NASA swallowed the annoyance over this, then recast the effort in a program to build a smaller and less ambitious suborbital demonstrator that would be built by OSC. NASA officials admitted that the original concept had been overly ambitious, since it was focused on a design for an operational system when a proof-of-concept vehicle was what was needed. First flight was scheduled for 1998. However, both the X-33 and X-34 programs continued to fall behind schedule while costs rose, and as mentioned, they were both canceled in March 2001.


[8.4] HL-20 / X-38 / X-37 / DREAMCHASER

* Although NASA dropped flight tests of lifting bodies in the mid-1970s, the agency didn't abandon the idea, returning to it in the late 1980s as an element in a study of a spacecraft launched by expendable booster to deliver up to eight passengers, again along with two flight crew, to a space station, and then act as a "lifeboat" for station crew rescue. The spacecraft was known as the "Crew Emergency Return Vehicle (CREV)" or "Assured Crew Return Vehicle (ACRV)".

HL-20 mockup

Concepts examined included a conventional space capsule design, as well as an "HL-20" lifting body. NASA worked with North Carolina State University and North Carolina A&T University to come up with a design for the HL-20 and produce a full-scale mockup, which was rolled out in 1990. Somewhat surprisingly, its configuration was much more reminiscent of the Soviet Lapot lifting-bodies than any of the NASA prototypes.

* The HL-20 itself never went beyond mockup evaluation, but in 1995 NASA went on to investigate a slightly more modest concept in the form of the "X-38", originally the "X-35", a lifting body very specifically modeled on the old Martin X-24A, to serve as a seven-person "lifeboat" from a space station. In 1995, the Scaled Composites Company was given a prototype development contract, constructing two unpowered 80% scale uncrewed aerodynamic test airframes.

X-38 test drop

Tests drops were conducted from the NASA B-52 carrier aircraft from 1999. The demonstrators had the interesting feature of popping out a large parafoil for landing as a means of substantially reducing landing speed. Scaled Composites was working on an orbital demonstrator when the program was canceled in 2002.

* Although these exercises were discouraging, in 2010 the USAF finally managed to put a spaceplane, a remote descendant of the X-20 Dyna-Soar, into orbit. The Air Force's robot "X-37B Orbital Test Vehicle (OTV)", launched as a payload on an expendable booster, was seen as a prototype for a "Space Maneuvering Vehicle (SMV)", an operational spaceplane that could perform a wide range of space missions, such as surveillance and rapid deployment of microsatellite constellations in a crisis -- a notion generally referred to as "operationally responsive space (ORS)". Little was said about long-range fast-reaction strike, but it was clearly an option. The SMV was to be capable of being "turned around" for a new sortie in as little as three days.

The X-37B program had complicated roots. It was initiated by NASA in the late 1990s; the original X-37 spaceplane was envisioned as a testbed for future spacecraft designs, with the vehicle sent into space as a shuttle payload. Boeing was the prime contractor, with the company contributing funding, while the Air Force Research Lab (AFRL) was also a "minority contributor" to the effort.

X-37 & X-40A

An unpowered subscale glide demonstrator, the "X-40A", was built and dropped from a carrier aircraft on tests from 1998. NASA and Boeing did work on a full-scale X-37 demonstrator and performed similar drop tests, but in 2004 NASA passed the program on to the Defense Advanced Research Projects Agency (DARPA). The AFRL remained involved; in 2006, the USAF finally decided to take ownership of the effort, under the direction of the Air Force Rapid Capabilities Office (AFRCO). DARPA and NASA remained as "minority contributors".

As it emerged, the X-37B had a bullet-shaped fuselage, stubby low-mounted "double delta" wings, and a vee tail. It had a launch weight of about 5,000 kilograms (11,000 pounds), a length of about 8.8 meters (29 feet), a wingspan of about 4.6 meters (15 feet), and a height of 2.9 meters (9.6 feet). The spaceplane had an orbital maneuvering system using storable hydrazine and nitrogen tetroxide propellants powering a single AR2-3 rocket engine with 31 kN (3,175 kgp / 7,000 lbf) thrust. The spacecraft also featured advanced thermal protection tiles and carbon-carbon materials to protect its aluminum and carbon-composite skin during re-entry, as well as tricycle landing gear -- the main gear with single wheels, the nose gear with twin wheels -- and a payload bay with double doors on the back. It featured an autonomous flight control system.


There have been four flights of the OTV:

* In the wake of the Obama Administration's push for development of commercial space, in response to the NASA CCDEV effort, Sierra Nevada Corporation (SNC) of Baltimore, Maryland, proposed a crewed lifting body with seven seats named the "DreamChaser", derived from the HL-20, to be launched on an Atlas 5 or other expendable booster for crew service to the ISS. SNC has performed aerial drop tests on models of the DreamChaser.

However, in September 2014, NASA awarded contracts to Boeing and SpaceX for their respective "CST-100" and "Dragonrider" capsules -- the Dragonrider being a crewed version of the existing Dragon supply capsule -- with the DreamChaser not making the cut. NASA did continue a degree of support for the DreamChaser, as per previous contract awards.



* In parallel with the initial flights of the X-37B, the Air Force was also performing preliminary studies on a "Reusable Booster System (RBS)" to replace the Delta IV and Atlas V EELVs from 2025, envisioning multistage launch vehicles with reusable primary stages that would cost only half as much as the EELV. Other studies were performed by the military for a small RLV system to support ORS launches. One such study performed by Northrop Grumman with Air Force funding produced a concept for a "Hybrid Launch Vehicle (HLV)", which would consist of a robot reusable winged vehicle carrying a small expendable booster on its back.

The HLV would be launched vertically, with the winged vehicle using rocket power to accelerate to Mach 7 and reach an altitude of 45,750 meters (150,000 feet), where the expendable booster would be released -- to either put a payload into orbit or send a conventional weapon downrange to a distant target. The winged vehicle would then fly back using some type of airbreathing propulsion, to land on a runway like an aircraft.

Northrop Grumman HLV

It would take no more than 48 hours to turn the HLV around for a new flight. Different configurations were envisioned for flying either medium or heavy payloads. Northrop Grumman estimated the HLV could cut launch costs by two-thirds compared to the use of a current expendable launch vehicle. However, due to funding cutbacks and concerns about technical feasibility the Air Force effectively dropped the RBS effort in late 2012.

The history of RLV development is long and dismal, but concepts like the HLV do seem more realistic now: a relatively modest RLV for small payloads, using an expendable orbital stage, seems within reach. It is the sort of configuration that NASA should have flown before proceeding on shuttle development. However, in a tight funding environment, even a modest RLV may be a hard sell.

* Concepts for SSTO RLVs have not died out, however. A UK firm named "Reaction Engines" has been floating around plans for an SSTO RLV named the "Skylon", powered by twin "Synergistic Air-Breathing Rocket Engines (SABREs)". Reaction Engines was set up by Alan Bond, who had worked on the HOTOL project; on its cancellation, he decided to strike out on his own to continue the work.

As envisioned at present, Skylon is a spindle-shaped vehicle with a length of 83.3 meters (273 feet) with a tailfin, small canard fins on the nose, short cropped-delta wings with a SABRE on each wingtip, a cargo bay between the wings, and tricycle landing gear. The SABRE is essentially a rocket engine that can use air for an oxidizer, operating effectively as a ramjet, or close its inlet and use a liquid oxidizer. SABRE will take off and land on a runway, fly to altitude, switch to pure rocket power to reach orbit, and then release a payload of up to 12 tonnes (13.2 tons). Although unpiloted, the Skylon could also be fitted with a passenger module carrying 30 to 40 passengers and a docking port for hooking up to the ISS.


Reaction Engines is currently working to develop a bench-test SABRE, the intent being to move on to the next stage of development once that is done, with flight of a demonstrator vehicle intended for 2018. While Skylon is a very intriguing idea, there has been skepticism -- once again focused on the "unobtanium" problem with SSTO -- not to mention the unencouraging history of a half-century of tinkering with SSTO RLV concepts. However, both the ESA and NASA have conducted reviews of the Skylon concept and given it a clean bill of health, at least on the condition that the performance goals intended by the SABRE engine are achieved.

* DARPA is now working on modest RLV under the "Experimental Spaceplane One (XS-1)" program. The XS-1 is envisioned as a reusable "first stage" vehicle that will carry an upper stage with a payload to the edge of space for launch. Payload is to be from 1,360 to 2,265 kilograms (3,000 to 5,000 pounds) into low Earth orbit, with a launch cost of $5 million USD per flight, on a launch rate of at least ten flights a year. DARPA will not touch SSTO concepts, DARPA official, earlier a shuttle commander, Pamela Melroy saying: "I banned the word single-stage-to-orbit from any discussion, instantly. We are not going there. We are not talking about it."

DARPA awarded three contracts in 2014 for preliminary design contracts, to lead to selection of one design for development of an XS-1 demonstrator. First flight is scheduled for late 2017, leading to an orbital flight test in 2018. The test program will involve ten flight in ten days, followed by putting a demonstration payload into orbit.


DARPA has generated a straw configuration, with a winged RLV first stage about the size of an F-15 Eagle fighter, powered by twin SpaceX Merlin 1D rocket motors. Total take-off weight is 102 tonnes (112 tons), including a upper stage weighing 6.8 tonnes (7.5 tons) with payload. The upper stage is expected to cost no more than $2 million USD. DARPA officials believe that it would be straightforward to scale up the XS-1 design to handle greater payload weights. Ironically, the XS-1 sounds like what NASA should have done as a first step, before proceeding on the shuttle -- but politically, that couldn't have happened, and it didn't happen.

* SpaceX is also working on a reusable derivative the Falcon 9 booster. After launch and second stage separation, the primary stage flips around and performs an engine burn for a controlled descent, to land vertically on four pop-out legs. After release of the payload, the second stage uses a heatshield on its forward section to re-enter the Earth's atmosphere, to then use its engines for a vertical landing, just like the first stage. Musk also envisions a cargo or crew capsule that can perform a vertical soft landing.

SpaceX boss Elon Musk commented on the effort: "It's just a very tough engineering problem [but] I've come to the conclusion that it can be solved. And SpaceX is going to try to do it ... If you look at the cost of a Falcon 9, it's about $50 to $60 million. But the cost of the fuel and oxygen and so forth is only about $200,000. So obviously, if we can reuse the rocket, say, a thousand times, then that would make the capital cost of the rocket for launch only about $50,000 ... It would allow about a hundred-fold reduction in launch costs."

SpaceX reusable booster

Musk is restating a dream going back to the early days of the Space Age, and the road he is going down is littered with the wreckage of past dreams. The first attempt to soft-land the first stage, on a barge at sea, was on 10 January 2015; the stage managed to reach the barge, but crashed into it. However, technology does advance, and if history teaches some caution, a case can still be made for optimism. It would certainly be hard-hearted not to wish those working on innovative RLV technologies the best of luck.



* I never really planned to write a history of the shuttle program. In 2000 I began work on comprehensive history of spaceflight titled THE RISE & FALL OF THE SPACE RACE, which I planned to write as a survey without getting into too much detail, particularly for the crewed space program. Unfortunately, the scope of that effort gradually increased with every installment that I wrote, until I found myself writing a much more detailed history than I had originally planned.

I had realized that if I wanted to write a credible survey, I had to have a provably good grasp of the details. The problem was that adding all these details to SPACE RACE, I saw that it was gradually becoming cumbersome and, ultimately, completely unreadable. The solution was to write a set of independent documents on various elements of the topic -- the shuttle program, the space station program, booster developments, military space efforts, different categories of satellites, international space programs, and so on -- that discussed the technical and operational details, allowing SPACE RACE to focus on politics and history. Readers of SPACE RACE could then go on to the specialized documents if more detail was desired.

While I am sure I will need to make corrections and add details here and there over time, this document contains about all I want to know about the shuttle program. After crunching through the matter from front to back I am left with the uneasy feeling that, although the shuttle was a remarkable machine with impressive capabilities, it still seemed to be an expensive solution in search of a problem, an unexciting exercise that in itself suggested no real future for humans in space. Hopefully, the new world that follows after the shuttle will prove more inspiring.


* Sources include:

Quite a bit of material was picked up here and there from the wide range of NASA handouts on the shuttle program.

* Revision history:

   v1.0.0 / 01 mar 11 
   v1.0.1 / 01 mar 13 / SpaceX reusable booster, more X-37B flights.
   v1.1.0 / 01 feb 15 / Various progress updates from 2013.