SINGLE STAGE TO ORBIT (SSTO) VEHICLES

NASA's vision for an SSTO,
circa mid-1980s.

Roton
Tech Level: 10
Michelle
Tech Level: 11
Nova and Thunderbird
Tech Level: 11

This article concentrates exclusively on VTOL (Vertical Take-Off and Landing) SSTOs. Rocket Planes and Scramjets are also types of SSTOs, but are discussed in their own seperate sections.

SSTO BASICS

When space rockets were first envisioned by early SF creators and rocket experts, they were almost always Single Stage To Orbit (SSTO) vehicles. Sleek finned vehicles that could travel into space and perhaps even to other worlds and return without having to shed significant amounts of their structural mass on the way. However, as the realities of interface travel sunk in during the early space age, multi-stage rockets were found to be much cheaper, more powerful, and reliable. Still, the allure of an SSTO was hard to squash, and in fact designs for them were in various stages of development all throughout the space age, but because of varying political, economic, and technical factors none of them ever reached even the scale-model testing stage.

Today, however, advances in material and propulsion technologies, as well as the need to reduce interface travel costs by any means practical, have led to the reflowering of SSTO interest and development. A number of them have even been tested.

An SSTO’s main purpose is to provide a reliable workhorse vehicle to routinely launch payloads into Low Earth Orbit (LEO) for as little money as possible. They must be reusable, powerful, fuel efficient, and light enough to lift a significant payload (at least 1000 kg) to LEO, and must be able to survive rentry and initiate a soft landing.

Early SSTO designs from the 1960s, 70s, and early 80s attempted to use what was then off-the-shelf technology. The most interesting were the manned Osiris vehicle from the mid 70s, which envisioned a sleek, cone-shaped manned vehicle propelled by an aerospike rocket engine, and the "mixed mode" series from the 80s, which featured different specialized vehicles using a dual fuel system of hydrogen and propane and 24 modular conventional rocket engines. Both were offshoots of the long-running but poorly supported Phoenix SSTO design project.

The progression of various SSTO concepts developed by NASA.

These along with nearly two dozen other designs that were developed over the decades were all feasible and most probably would have flown if built, but the SSTO concept met continually with resistance from a conservative aerospace community until after the Challenger disaster and the political wind-change that followed.

The first and most successful SSTO yet tested was the DC-X, also called the Delta Clipper. A very simple cone-shaped design that launched and soft-landed via its retro rockets, it flew 12 times between 1993 and 1996 before the project was transferred from the Department Of Defense to NASA, which promptly cancelled the project after the test vehicle suffered various mishaps.

The DC-X on the launch pad and undergoing a test flight.

ROTON

Tech Level: 10

The Roton was an intriguing project under development by private interests until a lack of funds killed it in 2000. Still, the technology held promise, and may resurface in the near future. It made 3 successful in-atmosphere test flights in 1999, proving the feasiblity of the concept.

I’ve read two different descriptions of how this vehicle is supposed to work. Both are given below.

The simplest is that the rocket is launched vertically using a rotary rocket engines, ie, rocket engines whose exhaust is angled in such a way as to make the whole rocket spin. The centrifugal force from this is used to spin a central shaft which is used in the descent phase, and is also used to help pump fuel into the engines. After delivering its cargo in orbit it deploys helicopter-like rotors on top of the vehicle. The Roton then descends and goes through re-entry bottom-first, the rotors canted upward to avoid the heat corona. After it reaches the atmosphere proper, its rotors kick in, passively at first, then powered by small rockets at the rotor tips. These small rockets are provided with fuel by the centrifugal force created by the rotating central shaft spun during the lift-off phase. The Roton then soft-lands much like a helicopter.

One version of the Roton's operation

The other scheme had the Roton employing its rotor from the beginning, using it very much like a propeller to assist during lift-off, taking a great deal of the load off the rocket engines and thus conserving on fuel. At about 6 miles up, the rotors begin losing their efficiency due to the ever decreasing air pressure, and the rocket motors take over completely. The rotor blades cant upward, still spinning to provide centrifugal pumping needed in the descent phase. The re-entry and descent sequence is essentially the same as described above.

The full-scale Roton vehicle like the one that was flight tested, if ever put into full operation, would be about 50 feet in height and could have delivered about 2.5 tons to orbit.


MICHELLE

Tech Level: 11

The MICHELLE SSTO concept, on launch and with aerobraking shroud deployed during descent

An interesting SSTO design being developed by TGV Rockets. It uses conventional rocket engines to achieve a height of about 100 km, with a payload capacity of about one ton. It undergoes reentry vertically, using the familiar retro rocket scheme for a soft landing. Michelle’s most intriguing innovation, however, is its aerobraking shroud. During ascent the shroud remains folded against the main body of the rocket. When it reaches significant layers of atmosphere during descent, however, the shroud deploys outward, looking very much like an angular tulip flower. The shroud acts much like a parachute but is much more dynamic and controllable.

The Michelle team also proposes using kerosene as the vehicle’s primary fuel.


NOVA AND THUNDERBIRD

Tech Level: 11

The Thunderbird is a modular vehicle designed to carry up to three people to about 100 km altitude. The Nova is a scaled-down one-man version, about 2/3 the Thunderbird’s 52 foot length, designed to be the world’s first privately-owned manned space vehicle. Both are in development by the Britain-based Starchaser Industries.

The ships have several interesting features. First is its modular design, consisting of a command module which includes crew quarters, guidance, and life support, and a propulsion module, which contains engines and fuel. Both sections seperate after orbital insertion and re-enter Earth’s atmosphere independently, making recovery, maintenance, and turn-around time easier and more efficient.

The ship re-enters using the familiar retro-rocket scheme, but in this case assisted by a steerable parasail deployed in the latter part of descent.

Both models are also designed to use kerosene as their primary fuel.


RELATED INFORMATION


A history of NASA's SSTO efforts:

http://www.spacefuture.com/archive/history_of_the_phoenix_vtol_ssto_and_recent_developments_in_single_stage_launch_systems.shtml

NASA's DC-X Homepage:

http://www.hq.nasa.gov/office/pao/History/x-33/dcx_menu.htm

Two detailed articles on the ROTON:

http://www.edgereview.com/ataglance.cfm?category=edge&ID=13
http://www.spacefuture.com/archive/the_roton_concept_and_its_unique_operations.shtml

TGV Rockets, Inc., and the Michelle Homepage

http://www.tgv-rockets.com/

Starchaser Industries and further information on the Nova and Thunderbird

http://www.starchaser.co.uk/



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