Private enterprise is driving the future of space transport with a wealth of reusable launch vehicle concepts
From man's earliest forays into space up to the arrival of NASA's Space Shuttle, every launch, manned or unmanned, necessarily destroyed the launch vehicle. Even today, the Shuttle is the only operational, partially reusable, launch vehicle in the world.
But 18 years after astronauts John Young and Bob Crippen piloted the Shuttle Columbia back to earth at the end of mission STS-1, US companies are promoting new reusable launch vehicle (RLV) concepts.
Projected development costs range from the optimistic - $150 million for the Rotary Rocket Roton - to the extravagant - $5-8 billion for the Lockheed Martin VentureStar development of NASA's X-33. Concepts cover vertical launch, horizontal take-off, single- or two-stage to orbit (SSTO or TSTO) designs, and have won varying sums of financial backing.
But a common approach, certainly among companies that do not enjoy government backing, is to keep it simple. In the words of Kelly Space and Technology president and chief executive Robert Davis, the philosophy is to develop a "leading-edge concept assembled of trailing-edge technologies".
Kelly's proposal is the Astroliner, now under development at the company's base in San Bernardino, California. The Astroliner is a piloted, partially reusable TSTO vehicle designed to be operated from any conventional airfield with a runway longer than 3,000m (10,000ft). It is intended to carry payloads of up to 4,770kg (10,500lb) to low-earth orbit (LEO), or up to 2,950kg into a 90¹ polar orbit.
Davis believes the horizontal take-off concept gives the vehicle an edge over rockets needing a dedicated launch site. "The cost and time to develop and place into operation a ground-based vertical launch site capability is prohibitive and lengthy," he says.
Kelly's approach to the RLV concept involves using a Boeing 747 to tow the fully fuelled Astroliner "aero-spaceplane", much like an aerotow glider launch, up to a predetermined air-launch point at about 20,000ft (6,000m). The launch site can be 1,600km (1,000 miles) or more from the take-off site, says Kelly.
Once released, the Astroliner can boost itself up to about 300,000ft using three Russian NK-33 liquid oxygen/kerosene reusable rocket engines. At this point, the engines are shut down and the vehicle continues an unpowered ballistic ascent. Passing through 400,000ft, the nose payload bay door opens, expelling the internally carried expendable upper stage and satellite payload combination.
Once clear of the Astroliner, the upper stage ignites and carries the satellite into orbit. The Astroliner, meanwhile, re-enters the atmosphere at about one-third of the Space Shuttle's speed - reducing thermal loads on the airframe - and glides down to about 50,000ft, by which time it has decelerated to subsonic speeds. It then ignites its four General Electric F414 turbine engines and flies under power as far as 925km (500nm) to its landing site.
"Towing to and launch of the Astroliner from an air-launch site eliminates the cost of the expensive ground-launch site infrastructure, saving approximately 30% of the cost of current launch systems," says Davis. "Reusability of the aerospaceplane eliminates an additional 30% of the current costs.
"[The Astroliner's] operation-has been carefully devised so as to fly and operate in regimes that do not push the state of the art or any flight envelope in any manner."
Davis believes the system offers low risk, a 40-60% reduction in launch costs and the ability to bring the launch system to the customer, rather than having to transport the payload to a remote launch site.
Kelly estimates it will need to raise $400 million to complete the first prototype Astroliner, but so far has raised only $10 million. Current planning has the 30-month development and construction of the first Astroliner complete in 2002, with flight testing to be finished in early 2003, followed by entry into service. About $100 million more will be required to build a second vehicle, says Davis.
Kistler Aerospace, based in Kirkland, Washington, meanwhile has had more success in raising funds for its K-1 vertical-launch TSTO rocket (left). By early May, the company had raised $450 million out of the estimated $750 million needed to build five K-1s and two spaceports.
Taiwan's finance ministry has given its approval for a group of Taiwanese banks to invest in the programme (Flight International, 2-8 June). Kistler is believed to have offered parts supply contracts and technology transfers to Taiwanese firms after its partners pledge $50 million to the K-1 programme. Having already raised some of its funds in Taiwan, Kistler is understood to be hoping to find a further $50-200 million in that country this year.
According to Kistler chief executive George Mueller, the K-1's maiden flight is scheduled for next year, having been delayed from 1998 because of funding problems. Kistler has already won approval to build the world's first commercial spaceport at Woomera, Australia, for this launch.
The K-1 is a fully reusable TSTO rocket designed to launch constellation satellites into LEO and some lighter payloads to geostationary transfer orbit (GTO). After separation from the second stage, the first stage returns to its launch site under its own power, and lands using parachutes and airbags. After deploying its payload, the second stage remains in orbit for 24 hours, then re-enters and returns to the launch site autonomously, again landing using parachutes and airbags.
After recovery, the two stages are inspected, mated again and are ready for launch with a new payload in nine days, says Mueller.
Costs are kept down by minimising the number of ground personnel required for a launch, and using low-cost expendables. The propellants for the vehicle are relatively cheap - liquid oxygen and kerosene - as are the pneumatic stage separation bolts, attitude controls and airbag inflaters.
Manufacturing costs are kept down by maximum use of off-the-shelf components, such as the vehicle's NK-33 and NK-43 engines, which are to be refurbished by Aerojet. The triply redundant computer system from AlliedSignal was originally developed for the X-33, and the Draper Laboratories software is based on the same company's Space Shuttle software.
Kistler also believes that the vehicle's repeated use will bring insurance premiums down almost to aircraft insurance levels.
Pioneer Rocketplane, based at Vandenberg AFB, California, is also concentrating on controlling risks in its Pathfinder aero-spaceplane programme. According to Pioneer chief executive Mitchell Clapp, the aim has been to avoid technical, regulatory, market or financing risks.
The first risk is avoided by adopting a "no new technology" policy and buying off the shelf where possible. The second requires a system that works within current flight regulations. According to Clapp, the last two risks mean that: you cannot assume 50 launches a year, many new markets or a single large customer; you should not sell all your equity too early; and you should not base your programme on "naive estimates of non-recurring cost".
Pioneer says it needs $300 million to build the first Pathfinder, and has raised $5 million to date. It says its vehicle is really an aircraft with rocket-like features which takes off under its own power, fuels up with liquid oxygenin flight and carries small and medium payloads. These are boosted into LEO by an expendable upper stage released from the vehicle's cargo bay.
Take-off and atmospheric flight will be powered by air-breathing General Electric F404 jet engines, says Clapp. The vehicle will be boosted into orbit by a single Pratt & Whitney/ Energomash RD-120 rocket engine generating 812kN (182,500lb) of thrust. The reaction control thrusters will be of the type originally designed for the Russian Buran space shuttle, to be built by Aerojet.
The Pathfinder will have the same digital flight control computer as the Boeing C-17 and the cockpit will be fitted with Boeing Aces II ejection seats.
The only untried element of the mission profile is the inflight liquid oxygen transfer, although Clapp says there are many precedents which suggest this process will be only a minor evolution from existing inflight refuelling practices. He points out that liquid oxygen is already moved inflight on every Space Shuttle mission - from the external fuel tank to the orbiter - and used to be transferred inflight into the X-15 hypersonic test aircraft before its launch from the B-52 carrier aircraft. Hands-off, automated liquid oxygen connections are also made in Zenit/Sea Launch operations.
In-flight liquid oxygen transfer trials are expected to take place by the end of this year, says Clapp. These will involve the transfer of 950 litres of liquid oxygen at a rate of 760 to 1,520 litres/min, from one Grumman A-6 with an underwing liquid oxygen tank to another with an underwing receiver tank.
The Pathfinder's upper stage will be based on off-the-shelf components, says Clapp, and powered by a 110kN (25,000lb)-thrust rocket engine derived from the Fastrac liquid oxygen/kerosene engine developed for NASA's X-34 RLV technology demonstrator.
Alongside the liquid oxygen transfer tests, Pioneer engineers are preparing for windtunnel tests and other hardware demonstrations, as the company continues to seek financial backing for a 2001 flight test date.
Rotary rocket plans
Rotary Rocket, of Redwood Shores, California, is reported to be in talks on funding for its Roton RLV with UK billionaire Richard Branson, founder of the Virgin business empire. Branson is understood to have an eye on the future potential of space tourism, and registered a new company, Virgin Galactic Airways, in April.
Virgin executives hope the new company could be offering space travel to wealthy tourists in about 10 years' time. Speaking at the Paris World Summit on the Space Transportation Business in May, LunaCorp president David Gump - representing Rotary Rocket chief executive Gary Hudson - said the manufacturer sees "billionaires who have a personal interest" as the biggest potential source of funding for the Roton programme.
To date, the company has secured $31 million of the estimated $150 million it needs to build and launch the first prototype, due for its maiden orbital flight in late 2000.
The Roton is a manned, vertically launched SSTO vehicle designed to carry satellites into LEO, medium earth orbit (MEO) or geostationary orbit (GEO). It will be launched under rocket power from the company's $2.5 million manufacturing and flight operations site at Mojave, California, and will return under rotary-wing power, with its rotor blades deploying on re-entry.
Hover testing of the $2.8 million Roton Atmospheric Test Vehicle (ATV) is about to begin, and the vehicle should be flying up to 8,000ft by the end of the year. Ground testing of the main rocket engine is due to start in July, continuing through to March 2000, with ground-based structural testing of another test vehicle due to run from July to December.
A sub-orbital prototype test vehicle (PTV) is scheduled to fly to an altitude of 96km (60 miles) between September and December next year, after which the first orbital PTV will be tested at up to 250km altitude between December 2000 and March 2001. This event is scheduled to be followed by entry into service in the same year, says Gump.
Houston, Texas-based Starcraft Boosters is looking for partners to develop its StarBooster 200 RLV concept. Taking a sideswipe at Lockheed Martin's technically troubled X-33, Starcraft chairman and former Apollo 11 astronaut Buzz Aldrin says the SSTO concept is not yet technologically feasible.
"X-33 flights will refine and demonstrate many important technologies," he says. "However, I do not believe that a scaled-up commercial derivative of the X-33 will be built within the next decade, maybe two."
Aldrin's interim solution concept is a reusable booster that can be mated with existing expendable launchers - as a payload multiplier - or with reusable orbiters, to create a cost-effective TSTO system.
The StarBooster 200 is essentially a hollowed-out, jet-powered aircraft with an empty weight of some 31,800kg (70,000lb), which can accommodate a Zenit or Atlas 3 first stage. The company had been hoping for backing for the concept from Lockheed Martin or Boeing, but Aldrin believes he is up against the manufacturers' attachment to the current Evolved Expendable Launch Vehicle programmes - which offer guaranteed near-term profits - as well as their own RLV concepts. As a result, the five-year old concept has yet to draw any financial backing.
Aldrin says development and construction of the first three StarBooster 200 vehicles would cost about $1 billion, and test flights could take place as early as 2001 or 2002, with entry into commercial service a year later.
By far the most ambitious and expensive of all the RLV concepts is the $5-8 billion, Lockheed Martin-led VentureStar SSTO development of the half-scale X-33 test vehicle. NASA has funded the X-33 sub-orbital technology demonstrator to the tune of $1 billion, with a further $270 million coming from Lockheed Martin and other partners, but the programme has now hit technical problems which have delayed its first flight until the middle of next year.
The VentureStar is designed to be launched vertically, powered by a revolutionary Boeing Rocketdyne linear aerospike rocket motor. It should be capable of carrying a 25t payload to LEO, 8t to GEO or 5t to polar orbit.
With the engine suffering development problems, Lockheed Martin admits that it seems a full-sized VentureStar would need strap-on boosters to reach orbit. Company chief executive Peter Teets also admits he has so far failed to attract private investment to the programme, admitting that it will need government funding or loan guarantees for the project to go ahead.
A decision to proceed could happen in the second half of next year at the earliest. The VentureStar could then begin flight tests at the end of 2004, entering revenue service in mid-2005. Dan Weldon, vice-chairman of the US Congressional space subcommittee, added his voice to the doubters earlier this year, however, saying he believes full development of the VentureStar is five to 10 years away - if the project ever happens.
To the other would-be RLV manufacturers, the VentureStar programme symbolises the hazards of aiming for a high-end, revolutionary solution to a technical challenge - a luxury seemingly available only to those with substantial government backing. Following their own more cautious route, the upstarts could instead end up realising a smaller, but real, advance in space transportation.