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Here's a great article describing the flawed shuttle design process, and hopefully engineers will take heed when the next manned launchers are created.
A few comments about the article, though, in that it leaves out a few drawbacks to the "ideal" system they have designed. The most important one is "coking," the tarring of hydrocarbon engines that makes them unattractive for RLVs. The NASA-MSC Fastrac engine was supposed to solve this, but I don;t think the engine was ever finished. The other was the inherently high mass/drag associated with reusable, flyback boosters. It would also be possible to parachute the boosters back in the same fashion as the SRBs, but NASA has done studies validating the economics of flyback boosters.
Interesting enough, a number of teams, including the Grumman-Boeing pairing, wanted to launch the shuttle on top of a Saturn V first stage as an interim step before the reusable first stage could be developed. J-2 engines would be used on a single-flight basis until the SSME was finished. Unfortunately, NASA decided in favor of an ET and segmented SRBs, which apparently have caused two fatal accidents out of 113 flights.
I truly believe that the shuttle would have been a much better vehicle if NASA and the Air Force had flown the X-20 Dyna Soar and gained experience in operating an orbital space plane before diving into the mammoth Space Shuttle. The shuttle is a remarkable technological achievement, but it never turned out to be practical.
By "our feet," I was referring to global society. I believe that the society sponsoring the space program must be unconditionally commited to any space effort. The goal here is to totally transform society into a space-faring civilization. Flying a few priveleged members of society a dozen times a year is hardly a space-faring society.
I really cannot blame NASA's engineers, and I probably would have made the same decision they did if I were in their position. All of the previous data from shuttle missions suggested that the tiles were strong and even the loss of a few would not have doomed the mission. If the extent of the damage were known, my preferred plan of of action would have been a shallower re-entry that would allow the crew to escape before loss of vehicle occurred.
The solution, expensive as it may be, is to put a space station in the 28.5 degree orbit instead of launching every shuttle to the current space station in 51.6 degree orbit. We have to remember that, right now, we're simply dipping our toes in the water in the grand scheme, the conquest of space. More space stations would represent getting our feet wet and making it impossible to retreat to the timidness of staying on earth.
ESA is now saying that two more Mars missions will be launched as part of Aurora: ExoMars and Mars Sample Return. ExoMars will launch in 2009, MSR in 2011 (probably ahead of the American effort, if current schedules and plans hold.) More info can be found in Space.Com's "Astro Notes." I wonder if the U.S.-French-Italian MSR effort will be the basis for the Aurora MSR.
The orbit chosen for STS-107 was optimized for its science payloads, particulary the Israeli-Palestinian dust experiment. Ironically, NASA had wanted to fly many of the experiments on ISS, but Congress wanted a dedicated Shuttle science mission to compensate for the under-utilization of ISS. On a similar note, STS-107 was to strengthen ties with Israel through launching its first astronaut.
I think that Shuttle Cam should be an essential safety feature when the orbiters return to flight. Other possible modifications could include changing the composition of the insulation, removing insulation from areas that are prone to shed it, and giving a reduced, four-person crew a set of encapsulated ejection seats (in case the crew had to reenter at a shallower angle that would not permit a safe landing.)
They might be out there. But it's too difficult to speculate about their capabilities, and the Air Force is being less than forthcoming with information about these so-called "black projects."
On Atlantis's last mission this fall, a camera was mounted on the top of the shuttle's ET. As far as I know, this camera was not installed on the subsequent flights of Endeavour or Columbia.
My line of thinking is that the suspected tile damage on Columbia would have been immediately detected if such a camera had been installed. NASA could then have decided on whether to abort the mission. If NASA had known about the tile damage during launch, however, they may still have decided to continue the mission and attempt re-entry instead of what would have been a dangerous launch abort. Nevertheless, I would feel better if this modification were made to all subsequent missions so this optionn is available.
The most accurate figures I've heard on the SR-71 was a top speed of Mach 3.5 (with Mach 4 possible, in theory, on a cold day) and a maximum ceiling of 100,000 feet.
Zubrin has some interesting comments on why the Blackbird is still the fastest in his epilogue to "Case for Mars." They make for excellent reading.
The OSP engineers have focused on an expendable launcher, and the participants on this forum have looked also at launch from a subsonic aircraft with an expendable fuel tank. But we need to ask ourselves whether we can do even better, and I believe the answer is yes.
I've done some basic calculations and I think that Bristol Spaceplanes has the right idea. Build an orbiter and mount it on a mothership which is essentially an SR-71 on steroids. The mothership flies on turbine / ramjet power to Mach 3 and 100,000 feet, then ignites a rocket and climbs to Mach 4 and outside the effective atmosphere. The orbiter would then ignite its engines and fly into orbit while the mothership descends and flies back to base. The beauty of the plan is that the orbiter only needs to be 65% fuel if kerosene propellants are used.
Such a system is possible with today's technology, but it would take over a decade for the industry to complete such a massive project. Whatever happened to the former attitude in America's aerospace industry, the one which designed and built the P-51 in 180 days? Or the one which took eight years to advance from suborbital flight to lunar landings? With the second world war and the cold war now a part of history, I feel that we do not have the motivation to undertake a major space development project at this time.
In addition to OSP, I can see the need for a new space capsule. An enlarged Soyuz (Zarya) was considered and rejected for ISS; Apollo shapes have also been considered.
I've been looking at a slightly-modified version of the proposed "Big Gemini." It would have ample room for landing skids and a parafoil landing system (Using the X-38 design instead of the original Gemini paraglider.) I feel that such a landing system is necessary because parachuting to a spot on the ground has its dangers (as the Voskhod 2 crew learned) and landng in the ocean makes it likely the crew will be lost at sea.
I don't think that this new "Big Gemini" would be reusable, and it would not be a replacement for OSP. But there are some missions where an expendable capsule is preferred, such as returning astronauts from earth orbit after a successful mission to the moon or Mars.
I do see a need for a vehicle that can safely return cargo to earth. The space station cargo is expensive hardware, and there is scientific value in being able to retrieve it. It may be possible, in the near future, to launch the Italian multipurpose logistics module on an expendible rocket and recover it with an inflatable heat shield. It's also possible to fly the shuttle in an unmanned configuration and perform this task, but the economics of this would be questionable at best. That's why I'm looking towards Kistler for this purpose. And, as reliable as Progress has been so far, it has limited payload capacity and is not reusable. I don't know whether the Kistler vehicle would be better suited towards delivering consumable supplies (like Progress) or scientific payload (like the shuttle.) But it still represents a capability that the ISS sorely needs.
I also think that cargo and passengers should be separate; my problem is with NASA's lack of a plan to replace the cargo tranfer abilities of Shuttle and, to a lesser extent, Progress. It's clear that OSP cannot adequately fill this mission. I hope that NASA will looks towards Kistler or somebody to fill this critical role.
Marcus Lindroos has a scathing review of the economics of OSP.
With MAKS, the only recurring cost is the fuel and ET. High flight rates are possible with the spaceplane, which will negate its small payload.
What should NASA do about this? I have an idea, although NASA probably won't pursue it:
1) Solicit a proposal from Molniya (or Molniya partnered with a major American firm) for OSP and recommend that MAKS be used as a basis.
2) The MAKS-derived OSP will initially be launched unmanned as an ISS lifeboat.
3) Such an OSP will utilize a robust (metallic?) heat shield and existing or near-term engines.
4) Within three years of the unmanned OSP flight, the MAKS-derived OSP will begin airlaunch test flights.
The info I got from Encyclopedia Astronautica indicates an 8.3 tonne payload to a 200 km orbit for the baseline MAKS. This payload weight would include a docking mechanism, so your payload delivered to ISS would be lower, but flying the orbiter unmanned would increase that payload to 9.5 tonnes.
Subsonic air launch gives MAKS a delta-V of about 270 m/s, but it also allows the spaceplane to reach all sorts of orbits and spares the expense of fixed launch sites. Clearly, air launch has tremendous benefits over ground launching once the technique is perfected.
MAKS was a promising development that was disappointingly killed by the Russian economic crisis. In reality, it should have been developed in place of the Buran, which was bound to inherit many of the problems that plagued the American Shuttles. Because much of its enabling technologies had been developed for Buran, the only big question mark was the tri-propellant engines.
Hopefully the money to revive MAKS will come, from either the space tourism business, or from NASA / ESA. It might need to be redesigned to use conventional bipropellant engines. But the basic design philosphy is sound, and MAKS could provide ISS with a low-cost, highly-flexible replacement for the Shuttle (on crew transfer flights) and Progress (on resupply missions.)
It's too early to say whether the fragile nature of Columbia's heat shielding caused its destruction, but I do agree that an alternative to these various ceramic tiles must be found. Boeing's been talking about composite heat shields for their X-37, but I have to say that metallic heat shields make the most sense (unless somebody comes up with an ablative paint that can be easily stripped between flights.)
Returning back to the original topic of the thread, air-launched RLVs, there is one significant problem that has to be worked out. Someone needs to find a means to shift the CG from a boost position to an aftward glide position. This is not a problem with the baseline MAKS because the propellant mass is stored in a front-mounted expendable tank. But the fully re-usable Maks-M will undoubtedly have issues with this, as have all totally-reusable vehicle designs.
It's also possible that ESA will buy into OSP and launch it with the Ariane 5 booster. And even assuming that two small OSPs could be launched cheaper than one, I don't think NASA likes the idea of tying up both docking ports with rescue spacecraft.
I don't think that OSP is the answer for replacing Progress freighters. A vehicle like the Kistler K1 would be best, assuming Kistler can get the funding and begin testing. I see the Kistler vehicle as a progressive step towards full reusability and routine space access.
I always thought that the goal of OSP was to replace the various crew-transfer craft like Shuttle and Soyuz with a safe, inexpensive and reusable vehicle. It doesn't make sense to launch both a Soyuz and a lightweight OSP when both launches can be combined into a single, heavyweight OSP launched by a heavy EELV.
And if NASA is unwilling to commit to a six-man, scientific space station, we should fund neither ISS nor OSP. ISS has cost far more than we expected, and its science return is smaller than expected due to cutbacks in crew and habitable volume. The taxpayers are being asked to front the costs for OSP because it should remedy the situation. But if NASA wants to stay with such a minimalist station, they should forget about it and quit wasting money on this boondoggle.
NASA came out with specs for the OSP today and they'r a bit underwhelming. I'm particularly disappointed that the vehicle is only required to have a crew of four (In the Orbital Sciences concept, there are two pilots and three astronauts, leaving little chance of a six-man ISS.)
I expect OSP to resemble a lifting body (such as the HL-20 being promoted by Orbital) or a delta-wing glider like Hermes or the Dyna-Soar. I doubt that air launch will be considered for OSP, but it might be a possibility for the "shuttle successor" that will come around in 2020.
John Pike has some fairly encouraging things to say about the economics of OSP on www.Globalsecurity.org.
Air launch for an RLV eliminates the need for new launch pads, but it poses additional problems. For one, a spaceplane will always be heavier than a rocket because it must be designed to resist bending loads from pitching maneuvers. And the fuel expended during the pitch-up maneuver negates the fuel savings of a subsonic carrier aircraft. This can be remedied if you used an airplane like a B-1 or TU-160 with a lot of thrust to release the RLV on a "toss-bombing" trajectory. But the carrier aircraft must also have room for additional fuel to replace the propellants that boil off inside the RLV.
This being said, I still support the development of an air-launched RLV. But I think that OSP will be developed faster if the designers stick with a lifting body mounted to an ELV, or perhaps a two-stage RLV system with a booster similar to the Kistler K-1.
I heard that some dudes (and chicks) in Australia are working on a SCRAM jet engine. I think it was for use in the atmosphere though, not as an engine to launch with.
That's the drawback to scramjets. They're totally useless outside the atmosphere. For this reason, Pratt & Whitney, Boeing, NASA, the Air Force, and everybody else in this field is focusing on Rocket-Based Combined Cycles and Turbine-Based Combined Cycles for operational aircraft and spacecraft.
For a brief but entertaining primer on combined cycle engines and hypersonic flight, I highly recommend Bill Sweetman's "Aurora: The Pentagon's Secret Hypersonic Spyplane."
You might be able to have a fast reactor inside the NTR to breed fuel, but a more feasible idea might be pyroprocessing the spent fuel from the reactor at a separate facility.
I think that a commitment to humans on Mars will wait until the years beyond 2010, after Jupiter Tour has validated the nuclear electric propulsion that will almost uncertainly be used in such an effort.
Project Prometheus is a politically safe way for the Bush administration to lay the groundwork for a Mars effort without the embarassment of SEI.
The only way to speed up this timetable is to adopt Mars Direct and utilize Russian Topaz reactors to provide power for the surface base.
Because OSP is designed only to launch crew and limited amounts of supplies, it is insufficient for the purpose of replacing the Shuttle. For near-term missions to bring supplies to the station (shuttle logistics module or Progress resupply,) NASA should consider pumping money into the Kistler K-1. The system is nearly complete and promises to make spaceflight cheaper than it is today for comparable sized payloads.
In the far term, NASA and the contractors should be thinking about a heavy-lift cargo RLV. The vehicle would be developed by the industry to tap into a commercial launch market that will have hopefully recovered by then. This vehicle would have a payload in the same range as the current shuttle and Delta IV/Titan IV/Ariane 5 series rockets. This RLV can be used for the assembly of future space stations or the assembly and servicing of reusble Mars shuttles.
I lke this talk of crew taxis, but I think that it makes more sense to use capsules instead of space planes for moving humans between LEO and either Lagrange Points or the moon. When NASA released its Mars DRM 3.0, it included a study of the tradeoffs between a capsule and an X-38 crew taxi for ferrying humans to a Mars spacecraft in HEO. The result was a weight savings around 10,000 kg for the capsule. Studies like this make me wish we'd have kept the Apollo capsule in production for use as a rescue ship or Earth Return Vehicle for future missions.
I think that even a spaceplane like OSP will be too expensive to replace every five years, and it will take more than five years for a replacement to come along. I think a ten-year cycle is more reasonable.
The problem I see with OSP is that NASA will own and operate the system. I don't believe that a manned spacecraft can meet the safety and cost goals unless it serves double-duty as an unmanned cargo rocket. Such rockets would be chartered by NASA rather than owned by NASA. Eventually, OSP will (hopefully) be mated with a reusable booster. The spaceplane will be NASA's contribution to the entire system, but the boosters should be privately-owned and the OSP privatized at the earliest possible date.