International Space Transportation System
Dual Propulsion ISTS Concepts
Brief History
The Root
ISTS Concepts
Ascent Roadmap

The first powered aircraft to fly twice was Wright Brothers Flyer No. 3 on 17 December 1903.  They were in the business of powered flight for what?  An hour?  We've been in the business of spaceflight for over 40 years; has a launch vehicle ever flown twice

Before This Decade is Out

- John F. Kennedy, 25 May 1961

This is an old document, last updated on 6 May 2006.  The modern Ascent Greenstar will be detailed elsewhere, it is completely different from what is described on this page.  The prices of development have been updated, and readjusted to 2006 dollars and more modern calculations.  Everything else was uploaded in April 2003.

1.                   Dr. Joseph Angelo wrote recently: One of the most important goals for the U.S. space program in the first decade of the 21st Century is to lower the cost of getting payloads into space.  Emphasis is therefore being placed on the development of a fully reusable launch vehicle (RLV).  This next-generation space lift vehicle will incorporate simple, fully reusable designs for airline-type operational techniques. (Encyclopedia of Space Exploration, Checkmark Books 2000, pp. 125 entry launch vehicle, Emphasis mine.) I hope this is a safe assumption.  The ideals are single stage to orbit (SSTO, or 1STO), runway take-off and landing, full reuse of major hardware (especially the lower stage(s)), and the ability to use international civil aviation methods for more airline-like operation.  Of these, the single-stage requirement is the most difficult to achieve, so I therefore have traded it off to advance the other three.

2.                   The basic mission in my study of these launch concepts is a 9,500 m/s  delta-v launch sequence not exceeding 10 minutes in duration from the launch pad.  Alternately, a 9,200 m/s delta-v from the Launch Entry Point (LEP) of  runway take-off vehicles, again with the launch sequence lasting 10 minutes or less from the LEP.  The LEP of runway take-off vehicles is at an altitude of approximately 12,000 m (40,000 ft) and a speed of about 400 knots.  This is where the countdown reaches zero for those vehicles.

3.                   For orbital rendezvous, by using the LEP as a synchronization point with a launch window of perhaps 15 seconds, it should be possible to achieve phasing (NC), altitude (NH), plane (NPC), and terminal intercept (TI) at ascent MECO (main engine cut-off) for a single orbit rendezvous that requires almost no upper stage maneuvering.  It may be possible to navigate to an LEP by using a plot from four aeronautical localizers used by civil aviation (airline-type operational techniques), rather than developing a new system (Navstar/GPS could also help in this area.)  The take-off window is about an hour because the launch vehicle can circle in a holding pattern near the LEP after taking off.

             To a space tourist what the above means is that you sit down in your spaceliner at almost any international airport and are docked at the space station within two to three hours, so you don't need a bed on your ship.  The Space Shuttle normally takes 42 hours from launch to dock with the ISS, and a typical flight from Sydney, Australia to Los Angeles takes about 10 hours.  Id guess the ticket would cost about $200,000 for coach.

4.                   In honor of our fallen Shuttles and their crews, reusable boosters in these concepts will be called Challenger and reusable orbiters will be called Columbia.



The Bluestar concept is the basis of an idealized two stage to orbit, runway operated fully reusable system capable of delivering a reusable orbital service vehicle with an 8,000 kg payload to a 9,500 m/s delta-v trajectory sufficient to allow docking with a spaceship stationed on a 52 degree inclination.  The launch stack takes off from a runway, the booster, Challenger stages at an altitude of about 55 kilometres, reenters the atmosphere and flies to a runway downrange of the launch site.  It should be small enough, quiet enough, and with low enough dry wing loading (therefore landing speed) to be able to land at any airport that can handle a wide-body airliner (but may need a special runway, at least initially, for take-off due to noise or take-off run.)  The much smaller Columbia produces its lift from its lifting body shape dominated by hydrogen propellant tankage.  Even with a payload, it should be able to land at more airports than the booster stage can.  Incidentally, the low mission cost of a runway launched and recovered fully reusable system may bring cost to low energy polar orbits low enough that replacing cellular phone systems with satellite phones may become practical as one of the many commercial applications of this concept.  Another commercial application for this concept is private space stations and space tourism.  For safety and for ferry purposes, Challenger needs to be able to land with an orbiter and payload, although venting propellants can be part of emergency landing procedures.  Columbia will need a gentle escape system (such as the Shuttles slidepole) as it may prove difficult to design her to land with boost propellants on board.  Both vehicles need backup recovery, as there is a possibility Columbia's propellants could explode before staging, destroying both vehicles.  Large stations can be launched by heavy vehicles derived from the Space Shuttle, such as the Shuttle-C or Shuttle-Z.

Bluestar is my personal favorite.  Its payload is fairly low for station assembly, but I believe that station assembly is best carried out with big 80 tonne or bigger chunks.  These can be handled by Shuttle-C, Shuttle-X or Energia, at a cost per launch similar to the current Shuttle.


Greystar is essentially a 40,000kg lift version of Bluestar.  The resulting launch vehicle might have a gross lift off mass so high that it simply can't be a Bluestar Plus, and we might need to get creative with orbiter processing facilities at airports to lift the larger Columbia.  It might be too noisy for all but the most remote runways, and might require take-off over desert or water to avoid environmental damage from its noise.  In order to keep take-off speeds feasibly low, one might need to get highly creative in order to reduce wing loading, perhaps using an excessive number of moving parts (flaps, slats, laminar vents, etc.) in order to create a wing system that will be able to lift the ship off the runway at low speeds and offer enough lift over drag (L/D) at high speeds and altitudes.

An alternative is to use pad take off, an idea already extensively analyzed during the late 1960's until 1972 as Phase A, Phase B and Alternate Space Shuttle Concepts programs of STS development.  The disadvantage of pad take-off is that it results in an even larger vehicle because the Thrust to Weight (T/W) ratio has to be greater than 1.0 to lift it off the pad, where it does not with runway take-off, as lift is generated aerodynamically and depends on L/D (i.e. a 5/1 L/D vehicle needs more than 1/5 T/W in order to lift off and accelerate in the air.)  This means that the pad take-off vehicle needs either much larger jet engines (probably too big) or rockets (real gas guzzlers.)  A possible profile for a pad take off booster is to build it with enough power to attain a transatlantic trajectory, after which it can be dead stick landed in Spain at one of the TAL abort sites for the Shuttle.  (I dont think this was considered for STS Phase A/B, in favor of flying back to the Kennedy Space Center.) 

Developing Greystar is best done using operational experience from Bluestar.  Greystar will likely need new facilities, despite being runway operated.  The orbiter will probably weigh 200 tonnes unfueled with payload.  This is quite a chew for mate/demate facilities and overhead cranes, and thats one of the simpler symptoms of Greystars enormity.


The Cyanstar is a partially reusable runway take-off concept.  It is able to deliver an 8,000 kg payload or Soyuz class orbital service vehicle to a 9,200 m/s delta-v trajectory sufficient to allow docking with a spaceship stationed on a 52 degree inclination.  One of the anachronistic features of the design of the STS Space Shuttle is that the lower stages are expended, not the upper stage.  The lower stage does not achieve orbital velocity, therefore does not endure an orbital entry and should be much easier to make reusable than the orbiter.  Also, the vehicle will be much more efficient because the wings and landing gear required only for landing when used on a pad-launched or second stage vehicle are not necessary on an expended orbiter.  In the Cyanstar concept the lower stage is reused and the upper stage is expended.  This removes a number of technical hurdles.  The flight regime of the Cyanstar booster is well known from X-15, HL-10, M2 and X-24  research.  The booster stage uses air breathing engines to the maximum speed and altitude that they can practically achieve, and then use a rocket system to get it out of the atmosphere to a staging height of 55 kilometres and a trajectory apex of about 70 kilometres.  After this, the booster reenters the atmosphere and lands at a downrange runway or returns to its launch site by flying on the air breathing engines. 

The upper stage, perhaps dropped out of a ventral bay (belly bay, like on a bomber) or launched from a dorsal bay (on the back, like on the Space Shuttle) can be one or more stages plus payload, which achieves orbital velocity.  An insertion profile like the Space Shuttles is recommended in this case to allow the last of the rocket stages to burn up in the atmosphere instead of joining the myriad debris currently on orbit.  (the Shuttle achieves an approximately 80km by target altitude orbit, followed by a circularization burn, often referred to as OMS-2, on the first orbit.  The external tank then burns up in the atmosphere after one orbit.)  I would not use hypergolic propellants, hydrogen peroxide, or liquid hydrogen on the Cyanstar upper stages because a rocket stage explosion in the Cyanstar bay would endanger the crew of the booster, even if they had an effective escape system or backup recovery.  LOX/Kerosene and Solid rockets are least likely to explode before ignition.

Space Shuttle: The History of the National Space Transportation System (all editions by Dennis Jenkins) details what happened early in the development of the Shuttle as its development budget was cut too far to allow the development of a fully reusable system.  Most ideas for lowering the cost of the Space Shuttle had involve replacing the flyback booster with some sort of expendable stage. (pp. 97) DoD requirements drove the size and capacity of the payload bay and the general planform via their high cross-range requirement. (pp. 99) What resulted was a vehicle which, by wise technical and practical reasoning, should never have been built.  Now, lets take a look at Cyanstar for a moment: Its payload does not need to be a manned spacecraft, although that is one of its options.  Cyanstars bay does not need to be restricted to one type of upper stage.  On its own, it can fly to about Mach 6 and 65,000 m altitude (215,000 ft).  Can you think of DoD applications of this type of vehicle? 

Ive studied Chinese and Indian launch vehicles; they use exclusively solid or hypergolic propellants (or combinations) known for their stability and storability suggesting a launch-on-demand function that is of little use in a true launch vehicle.  My opinion is (especially since finding out what the Long March is named after) that these are ballistic missiles using launch vehicle as a political cover for a military purpose.  US and USSR early launch vehicles (primarily Atlas and Semiorka, or R-7) were ostensibly missiles before they were launch vehicles, and both are still in service, but not as missiles (we need to remember this history if North Korea or Iraq starts developing space vehicles.)

Now, lets assume an air-launched ballistic missile (ALBM) is developed for Cyanstar.  Current ICBMs are protected by concrete silos, vulnerable simply because they don't move.  The ICBMs once launched, cannot be recalled, and even if destroyed by range safety (which can only be done for the first couple minutes), they are still lost and their radioactive material is scattered over friendly territory.  A Cyanstar can be kept on airborne alert, making it nearly impossible for an enemy to destroy, and because Cyanstar has a boost sequence, the launch can be aborted and the missile recovered up to four minutes after being ordered to fire.  If the DoD doesn't want to use the stages developed for Cyanstar, they can do a classified development of their own Cyanstar ALBM.  By putting it in a frangible launch container, no one even needs to know what it looks like until it's used in anger.  This is in addition to the more conventional uses of high altitude reconnaissance and bombing.  I'm pretty sure that Cyanstar would have been cheaper to develop than the production Shuttle, and a new high-performance ALBM platform would have made the Department of Defense happy, but as they say, hindsights 20/20. 

For the current time however, I do not believe that Cyanstar is appropriate unless were desperate.  Cyanstar need not resume manned spaceflight, but it will certainly reduce launch costs.  Also, if the Sprint program(q.v.) is implemented, it may be possible to design Cyanstar to be backwards compatible with the Delta Sprint spacecraft, thus further reducing development costs.  I sincerely hope that financial headaches that occurred with the Shuttle and ISS do not recur for ISTS, but Cyanstar is our last stand in case they do.

Greenstar (Legacy)

The Greenstar is the largest of these concepts, designed as a pad-launched partially reusable system to put 80,000 kg on the aforementioned 9,500 m/s trajectory designed around reaching a 52 degree inclination station.  Save Skylab, every major station has flown on this inclination.  Also, every assembly mission launched to this inclination has been a 20,000 to 40,000 kg class payload.  The first stage is a pad-launched, all rocket boosted stage with secondary air breathing engines.  There are two options for upper stage.  The first is an expended stage capable of lifting the full 80,000 kg, and the second is a reusable orbiter capable of lifting 15,000 kg.  The latter might be desirable for low cost logistics, and also to provide an robotic arm capability.  If both Bluestar and Greenstar are developed, this should not be necessary, as the Bluestar orbiter can provide those functions. 

The launch profile of Greenstar is that it will take off from a Kennedy Space Center LC39 class launch pad.  The first stage uses large rockets to carry itself and its upper stage to a downrange point at an altitude of about 45 kilometres and Mach 4, similar to the STS Solid Rocket Booster staging point.  This booster, made with large outboard engines and possibly smaller centreline engines could be made to fit the existing pad structures with little or no modification to the Mobile Launch Platform, Mobile Crawler Transporter, and flame trenches.  If centreline engines are used, these may be programmed to start in midair so that their exhaust does not impinge significantly on the pad structure.  After staging, the booster returns to subsonic stratospheric conditions, where it can use its secondary air breathing engines to fly back to the Kennedy Space Center runway.  The upper stage uses its rockets to achieve orbital velocity.  Because the upper stage does not include wings and wheels like the Space Shuttle, the overall size of this launch vehicle will be much similar to the STS stack.  Some modifications will be required for the RSS, FSS, OPF, and VAB.

Perhaps the most efficient means of developing the Greenstar concept is dusting off MSFCs MSC-001 DC-3 concept from 1970, actually considered for STS, and resuming its development. (Space Shuttle: The History...)  The technology for the essential major systems has not fundamentally changed since then (unless aerospike rockets are considered) and the only difference between that more detailed concept and the basic Greenstar is the consideration for using expendable upper stages.  The study masses from MSC-001|*Ibid*| suggest a combined expended stage mass and payload of 38,600kg using LOX/Hydrogen propulsion, which should still be adequate for station assembly modules.  The 6,800kg payload of the reusable orbiter in the MSC-001 concept is also adequate. 

Ideally, both Bluestar and Greenstar will form ISTS, with Bluestar being used primarily for crew transfers and logistics, while Greenstar provides for high energy manned missions (i.e. Moon, Mars, NEOs) and station assembly.


This is a list in order of estimated development costs, from cheapest to most expensive, of these concepts (I hope to get actual numbers for these concepts.  These numbers are wild guesses in US dollars and are hopefully on the high side.) 

1.                   Cyanstar $12 bln.

2.                   Legacy Greenstar (expended upper stage) $30 bln.

3.                   Legacy Greenstar (with manned orbiter) $40 bln.

4.                   Bluestar $30 bln.

5.                   Greystar $80 bln.

6.                   Space Shuttle $26 bln.*

7.             Ascent Greenstar $0.5 bln. 

September 2007 Note: I now believe that Ascent Greenstar is very inappropriate for its payload class; its replacement in the Ascent Roadmap (Lilmax) is probably in the ballpark of $4 billion to develop.

* According to Jenkins,Space Shuttle, 3rd Edition (Voyageur 2001) adjusted to 2006.