by Susmita MohantyNov 03, 2021
Early experiments with reusable rockets
In the late 1990s, when I began my professional aerospace journey in Southern California, Single State to Orbit (SSTO) launch vehicles were in the news. While preparing for a job interview, I remember reading about DC-X1(1), short for Delta Clipper Experimental, a one-third scale prototype of a reusable SSTO built by McDonnell Douglas with funding from the Strategic Defence Initiative Organization (SDIO). Three DC-X flights took place at the White Sands Missile Range (WSMR) in New Mexico in 1993. After that the funding ran out as the SDIO wound down.(2)
In 1994, NASA initiated the Reusable Launch Vehicle (RLV) program, which included support for an upgraded DC-X variant called DC-XA for a couple of years. NASA abandoned the DC-XA in 1996 due to technical problems and that same year awarded a contract to Lockheed Martin to build the X-33 SSTO experimental vehicle. Lockheed also announced plans to build a full-scale X-33 sequel called VentureStar. In 2001, NASA cancelled the X-33 program due to technical challenges and rising costs. Lockheed Martin promptly scraped VentureStar. The New Mexico Office for Space Commercialization (NMOSC) created in 1994 hosted DC-X flights at the WSMR and was keen on hosting the future X-33 flights from WSMR.(3)
The Ansari X-Prize
This early history of reusable launch vehicles and New Mexico’s keenness to host RLV flights is important in the context of the latest Branson flight from Spaceport America in New Mexico because I recall someone telling me back in 1997 that Branson was keeping an eye out for SSTOs. I have no easy way of verifying that memory now, but in October 2004 when the maverick aircraft designer Burt Rutan and his team of engineers at Scaled Composites, Seattle, won the Ansari X-Prize(4), it came as no surprise that Branson grabbed the opportunity that he had been looking for and commissioned Rutan to build him SpaceShipTwo (SS2). It’s predecessor, SpaceShipOne (SS1) crossed the finish line in an eight-year, $10 million private spaceplane race triggered by the Ansari X-Prize, winning the US$ 10 million prize purse with its second spaceflight in less than a week. At its highest point, the SS1 rocket plane reached an altitude of 367,442 feet (69.6 miles or 112 kilometres), easily topping the 100-kilometre (62.5-miles) altitude required to win the prize. SS1 was developed with a $28 million investment from the late Microsoft co-founder, Paul Allen.
The $10 million Ansari XPRIZE was designed to lower the risk and cost of going to space by incentivising the creation of a reliable, reusable, privately financed, crewed spaceship that finally made private space travel commercially viable.(5) Teams around the world were challenged to build a reliable, reusable, privately financed, manned spaceship capable of:
- Carrying 3 people
- To 100 kilometres about the Earth's surface
- Twice within 2 weeks
The Ansari XPRIZE was an inflection point in the history of human spaceflight. Thus far, spaceflight had been the exclusive purview of governments. The idea of private spaceflight was either frowned upon or considered too dangerous and expensive for the general public.
The epic journey from SS1 to SS2
On July 11, 2021, nearly 17 years later, VSS Unity made a successful, crewed suborbital test flight to 282,000 feet (86 kilometres) above Earth's surface before gliding back down to Spaceport America in New Mexico for a smooth runway landing(6). VSS Unity, the SS2 rocket plane carried two pilots and six passengers - Branson and his five crew mates.
Both SS1 and SS2 were designed by Burt Rutan, with VSS Unity employing the ‘shuttlecock’ atmospheric re-entry system pioneered by SS1. The launch approach is also the same, with the spacecraft carried aloft by a huge mothership. Both motherships nestled their rocket planes beneath wide-spreading wings. SS1’s mothership was called WhiteKnightOne, while the mothership for VSS Unity was christened VMS Eve in honour of Branson’s mother.(7)
Apparently, SS1 was designed by Burt and his crew at Scaled Composites in the early 1980s. The space vehicle was part of a broader program known as Tier One, which was made up of SS1, a launch aircraft called WhiteKnightOne, a hybrid rocket engine system using rubber and liquid nitrous oxide as the fuels, and an avionics suite. Scaled Composites had previously developed dozens of unique composite material aircraft. To launch SS1 directly from the ground would have required a great deal more fuel, nearly doubling the weight of the vehicle and making it difficult to reach space. For this reason, it was important to develop the WhiteKnightOne to take SS1 up to about 47,000 feet (14,000 metres) and drop it from underneath. The SS1 pilot would then light the hybrid rocket, which would send SS1 into a near-vertical trajectory.(8)
In November 2017, when I was invited by The Economist magazine to speak at their event 'The New Space Age' at the Seattle Museum of Flight(9), I remember teasing my friend and fellow speaker, George Whitesides, the CEO of Virgin Galactic that we have been waiting for over 12 years for SS2’s commercial debut. It took an additional four years from then, to make it happen. The friendly nudge I gave George in Seattle in an open forum needs a bit more of deep dive to understand why it took 17 years to get from SS1 to SS2 or to bring the SS2 from concept to commercialisation.
Rutan had to scale up SS1 significantly for SS2. SS1 was designed to carry a single pilot, plus enough dead weight to substitute for two passengers. VG started out with a design that would accommodate six passengers plus two pilots for a flight reaching SS1's target altitude of 100 kilometres (62 miles). But in the process of turning the design into reality, Virgin Galactic trimmed back the seating capacity to two pilots plus four in the passenger cabin, and went with a 50-mile target. Weight turned out to be a limiting factor for the development of SS2. Safety was the other big design concern. Here’s an overview of the SS2 development timeline by science and tech writer, Alan Boyle, that highlights the mishaps and safety issues that had to be addressed by the SS2 design team.
In July 2007, three of the workers involved in SS2 development died when a tank of nitrous oxide exploded at the Mojave test site of Scaled Composites10. In October 2014, nearly a decade after SS1 won the Ansari X-Prize, a test pilot died and another was seriously injured when the first SS2 craft, VSS Enterprise, broke up during a test flight(11). These fatal accidents reinforce that rocket science is never easy despite decades of technological advancements. Investigations followed leading to changes in the pilot training procedures and SS2 design. In December 2018(12), in February 2019(13), and in May 2021(14), the new rocket plane VSS Unity was successfully flown beyond the 50-mile mark. The first two flights took place at the Mojave spaceport in California and the one in 2021 happened after Virgin Galactic moved its base of operations to Spaceport America in New Mexico. The string of successful flight tests set the stage for Branson and crew to kickstart Virgin Galactic’s commercial operations this July.(15)
After a quarter of a century of successes, failures, aborts, restarts, human grit and technical genius, the RLV story that I had been following in my early days in Southern California had finally come full circle - from the first DC-X flights in 1993 in White Sands in New Mexico to the successful flight of VSS Unity in 2021 at Spaceport America in New Mexico. This was not only as an accomplishment for Branson and the Virgin Galactic team, but also for Burt Rutan and the Scaled Composites team, the X-Prize team, Paul Allen who funded SS1 and licensed it to Branson for SS2, Anousheh Ansari who wrote the check for the Ansari X-Prize, as well as the supportive citizens and successive administrations of New Mexico who did not give up on the state’s dream of hosting RLV flights that resulted in Spaceport America.
Noteworthy design features of rocket plane SS2
SS2’s most innovative feature is its capability to change its shape in space to ensure a repeatable safe re-entry. By rotating its wings and tail booms upwards while in space, the vehicle’s stability and rate of deceleration in descent is controlled by aerodynamic forces. This “feathering” design takes the best from both the traditional capsule and winged space vehicle designs, and adds a little magic of its own. The “feathering” concept is often compared to a badminton shuttlecock – and proves that sometimes the most disruptive designs can emerge from the most humble of origins.
SS2 is powered by a hybrid rocket motor – combining elements of solid rockets and liquid rocket engines. Both types of rocket engine have advantages; the hybrid aims to combine the simplicity of a solid motor with the controllability of a liquid. SS2’s rocket motor can be shut down quickly and safely at any point during the flight. With the exception of the rocket motor’s fuel and oxidizer, which must be replenished after each flight, SS2 is a fully reusable spacecraft.(16)
As an engineer and industrial designer, what caught my attention with the prize-winning flight of SS1 in 2004 was the fin design of the SS1. Only a aeronautical genius like Burt Rutan17 could come up with this spectacular aerodynamic fin design. What I like most about the SS2 is its streamlined cabin interiors, gorgeous bank of windows and seat ergonomics. While the interior volume is cramped due to engineering constraints of a rocket plane designed for a crew of eight, remember it expands into a three-dimensional space when the passengers get to free-float for a few seconds of weightlessness that they experience at the tip of the sub-orbital trajectory. Passenger-centricity is key when you have to fly paying passengers. They will not only want safety, but would also like to travel to space and back with a certain degree of style and comfort. Not to mention, the best views of their home planet below.
Era of casual space tourism has begun
After Branson’s debut flight in July, Virgin Galactic has reopened ticket sales for its space flights at a starting price of US$450,000 a seat. The firm hopes to start commercial flights next year after completing several more test missions. It had previously sold tickets at $250,000 apiece but stopped in 2014 after a fatal accident.(18)
Casual space tourism comes at a time when the world is reeling under extreme weather events and a pandemic. The sixth Intergovernmental Panel on Climate Change (IPCC) climate report(19) published this month warns that global heating is irreversible and issued its starkest warning that, unless meaningful action is taken to reduce emissions, the world is on course for catastrophic warming. Also, anthropogenic space debris(20) in near-earth space has reached disastrous levels. It is unlikely that space tourism companies will voluntarily go the extra mile to earn their green credentials. So, the global space collective should come up with enforceable environmental laws for these tourism companies to comply with.
Making space more accessible is cool, so long as we don’t lose sight of the environment and ensure that the passenger demographics is not skewed to include only the super-wealthy.(21)
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