The one possible exception is on-orbit satellite repair - but it will be hard to develop manned orbiting spacecraft that can carry out such repairs for a cost less than simply building and launching a replacement satellite on an unmanned booster.

And any useful materials we might be able to manufacture in Zero-G can also be manufactured more cheaply on unmanned satellites, and returned to Earth in unmanned capsules.

That's assuming that we can identify any such substances in the first place. Every single substance NASA has so far proposed to use weightlessness to manufacture -- whether drugs or alloys -- has turned out either to have no real use, or be far cheaper to manufacture using other techniques on Earth. Even after we finally do get launch costs far down below their current level, this may remain true.

But let's assume that occasions do turn up in the next couple of decades where manned orbital spaceflight IS justified. Let's also assume -- as is very likely -- that political pressures do cause the government to continue flying some manned Earth-orbital missions, ostensibly for such practical reasons, but in reality mostly for national prestige and the fact that the public does have a fair amount of interest in manned spaceflight. What should America's next manned spacecraft be like?

The proposed Orbital Space Plane unquestionably lacks some of the Shuttle's most serious weaknesses. It will definitely have an escape rocket system to yank the OSP off the top of a malfunctioning booster to safety -- and, since it's mounted on the top of its booster, its heat shield system won't undergo any pelting from chunks of material falling off the side of a fuel tank towering far above it. These facts by itself will make it far safer than the Shuttle.

But it's still likely to have another feature that NASA has long been peddling as a virtue, but which is actually a serious flaw -- wings. Wings look magnificent on a spacecraft, but the fact that they enable a runway landing is far less useful than NASA makes it out to be. And they have two significant disadvantages.

The first is safety. Any winged spacecraft must pancake back into the atmosphere belly-first, in order to spread out its reentry heating over a wide part of its surface rather than concentrating that heat on its leading edges so intensely that no substance we know of could endure the high temperatures without being hopelessly heavy.

But, by so doing, it becomes as unstable as a Frisbee flying through the air sideways -- it must constantly keep adjusting its control surfaces at very high speed to keep from tipping into a reentry attitude that would be more aerodynamically natural for it, but which would also heat its wing edges and pointed nose to melting point. If it falls off that delicate tightrope balance -- even for a second -- the result is disaster.

By contrast, capsules tend to naturally stabilize themselves bottom-down, keeping their main heat shields downwards into the increasingly dense atmosphere.

This fact saved the life of Yuri Gagarin, the first human in space, and his successors on three of the next seven Soviet manned flights. In each case, the rear service module failed to cut all its connector cables completely free from the capsule after retrofire, dragging the capsule back into the atmosphere at the wrong attitude -- until the growing aerodynamic forces finally ripped the service module free, whereupon the capsule, even without an active attitude control system, instantly and naturally tilted into its proper reentry attitude.

Also, any orbiting space capsule will have a jettisonable "service module" fastened to its bottom -- and that module will serve as an additional shield against small, high-speed bits of "space garbage" that might damage that particularly crucial bottom shield.

The heat shields on the capsule's sides won't be so shielded -- but they also have to endure considerably less reentry heating, and so can tolerate small holes from space garbage a good deal better.

And wings are also extra weight -- a lot of it. As veteran aerospace engineer Robert C. Truax, who had a key role in developing the Polaris missile, points out in his article in the Jan. 1999 "Aerospace America" (which should be required reading for anyone interested in the exploration and exploitation of space), turning any returnable space vehicle into a glider cuts its cargo payload by a factor of three.

This applies to reusable boosters, as well as to any recoverable payload vehicle they may launch into orbit: "It would be very difficult to improve on the cost-effectiveness of a...booster recovered in the ocean [near the launch site] by parachute and retrieved by tugboat. After landing, returning spent stages to base is cheap and quick, regardless of the size of the stage.

"The retrieval time of about 20 hours will be a small fraction of the turnaround time for many years to come, possibly forever, and it actually costs less to return the Shuttle's solid rocket boosters to Kennedy Space Center than to move the Orbiter from the landing strip at nearby Patrick AFB back to the launch pad...

"Putting wings on a space launch vehicle makes little economic sense: they are heavy, costly, and unnecessary... [And] using wings to recover from orbit costs a major fraction of the recovered weight, compared with perhaps 10-12% for an ablating heat shield and a parachute."

Since the Delta 4 and Atlas 5, which are the OSP's possible launch vehicles, can put only 20,500 and 23,000 kg respectively into a 28-degree inclined orbit -- and a good deal less into the Station's 51.6 degree inclined orbit -- the vehicle had better be made as light as possible.

This need has required NASA to lower its Level 1 design requirement for the OSP to carry only four people at a time -- making a pair of them necessary to evacuate the Space Station's crew in an emergency. Switching to a capsule design that could carry six or seven people with the same total vehicle weight (or less) would seem to be an eminently sensible move.

Moreover -- as Jeff Wright recently pointed out in SpaceDaily -- attaching any winged spacecraft to a rocket produces serious aerodynamic problems during the launch, because the natural lift from the wings is a force that is powerfully trying to drag the spaceplane sideways from the rocket.

The only way to counter this is -- as on the Shuttle -- to have the plane constantly and rapidly adjust its elevons to keep canceling out the varying degrees of this force. And that means that its EELV booster's own autopilot must be programmed to also control the spaceplane's control surfaces, further increasing the cost of any winged OSP system.

What are the supposed compensatory advantages of wings?

Well, NASA is currently debating whether to make the Orbital Space "Plane" a capsule, or to give it wings or make it into a lifting body to give it runway capabilities. According to the Feb. 24 Aviation Week, NASA is leaning toward the latter because of OSP's listed Level 1 design requirement to be able to deliver sick or injured Space Station crewmen to "definitive medical care within 24 hours."

But it is seriously doubtful whether runway landing capabilities are even needed for that. Pickup ships with both on-board medical capabilities and helicopter delivery to land-based hospitals could be planted not only at a capsule's normal splashdown point near the launch site, but at several emergency landing sites scattered around the world, at an operating cost still making such a system far more cost-effective than a winged OSP with a small payload (since such ships could carry out other functions during their long idle periods).

Or the nation's preexisting Navy and Coast Guard -- which, after all, must regularly pick up ailing people from all over the world's oceans -- could fill the need.

And that's just assuming that the capsule would have to land in the ocean rather than on land. It might well be designed for the latter, using airbags such as the Kistler Company plans to use to recover its booster's reusable stages, or retrorockets such as the Russians have used to cushion their capsules' landings since 1964, or even a deployable "paraglider" parachute that might allow a capsule to actually make a runway landing on deployable skids (such as was planned for the Gemini program, and cancelled despite a series of successful tests only because of cost overruns).

But a simple parachute landing -- on land, or even on water -- is also, on balance, far safer for the crew than any kind of runway landing, simply because it does not require precise guidance to touch down on a tiny spot, with a crash occurring if the touchdown occurs anywhere else.

In short, it's hard to avoid the suspicion that NASA, as usual, is frantically grubbing for fake reasons to make its latest manned space project a good deal bigger and more expensive than necessary.

The other argument often used against capsules is that, unlike winged vehicles, they are supposedly non-reusable. "Space News" says this in its March 3 editorial on the OSP (in which it says that a capsule design may well be preferable to a winged one anyway, being much cheaper and faster to develop). Nonetheless, Rep. Dana Rohrabacher of California, chairman of the House Science Space and Aeronautics Subcommittee, recently said, "From what I remember, capsules don't lend themselves to reusability."

But the U.S. first reused a space capsule 36 years ago! The capsule used on Gemini 2, an unmanned 3400-km suborbital test flight in Jan. 1965, was reused for an 8900-km suborbital flight in Nov. 1966 -- the only flight ever made in the later-cancelled Manned Orbiting Laboratory program.

The Gemini capsule would have been the Earth return vehicle perched on top of the MOL, and the Air Force wanted to make sure that the Gemini's heat shield would still function properly with a hatch cut into it to allow the crew to transfer between the two vehicles.

The Gemini capsules were not even designed to be reused, but the decision was made to do so to save costs, and the capsule came through both flights in perfect shape.

A capsule specifically designed to be reusable could do even better. It could easily be designed to endure the shock of either a water or dry-land landing, and its heat shield -- whether made out of burn-away ablative material, or super-insulating tiles like the Shuttle -- could be replaced much more easily than the tiles on the Shuttle can be repaired after each of its flights.

And as "Space News" pointed out, a vehicle as small as the OSP -- which is supposed to carry only crews, not cargo -- would cost little to replace even if it was NOT reusable, especially if it was a capsule instead of a much heavier and more complex winged vehicle. (After all, OSP's entire launch booster is supposed to be non-reusable anyway.)

The next major question is: what kind of launch vehicle should the US develop next, after the Shuttle and the new Evolved Expendable Launch Vehicles (Atlas 5 and Delta 4)?

Robert Truax's 1999 article on this is invaluable, both because its arguments are thoroughly convincing (most of them are based on elementary high-school physics) and because it's a well-arranged summary of the important points:

1. "To reduce the cost of a launch vehicle, minimizing its complexity is vastly more important than minimizing its size. The Agena upper stage cost more than the big Thor ICBM, despite being only one-fifth its size -- and the second stage of the Saturn 5, despite being one-fifth the size of its first stage, cost more to develop and only slightly less to mass-produce.

   "These two examples...are not flukes, but part of a general truth...Long-range rockets or space vehicles, even relatively simple ones, are highly engineered devices. The cost to do this engineering is almost independent of the size of the parts, but heavily dependent on the number of parts...About the only cost elements that vary more or less directly with size are raw materials and propellants, but these constitute only a tiny fraction of total launch-system price."

   [Thus, trying to force the development of new technologies just in order to build one launch vehicle (as NASA has repeatedly tried to do) will run up the cost of that vehicle enormously -- as compared to waiting until technologies have already been developed, and only then utilizing them to build a launch vehicle.]

2. Any sensible launch vehicle, for a long time to come, should be at least two-stage. Making rockets out of more than one stage makes just as much sense now as it always has. "Other parameters being equal, an SSTO [Single State To Orbit] vehicle can carry much less payload than one having two stages. A lot of dead weight has to be accelerated to orbital velocity at great cost, only to be brought back through the 'thermal thicket' at equally great cost."

   Strap-on boosters -- like those on the "1-1/2-stage" Shuttle -- should be avoided for the same reason: they're much less efficient than a 2-stage rocket.

   [Truax also believes that this design greatly further increased the cost of the Shuttle because its liquid-fuel engines must be designed to function at a wide range of air pressures from sea level all the way up to vacuum, vastly increasing their design complexity.]

3. Liquid-fuel engines are better for any large rocket than solid-fueled ones. Their reliability is comparable; their fuels cost only a few percent as much as solid fuels; they can be shut down if an imminent catastrophic failure is sensed (making an emergency launch escape easier for a manned vehicle); and, according to Truax, a properly-designed liquid-fueled stage that parachutes into the ocean can actually be repaired and renovated much more easily than a solid-fueled one like the Shuttle's boosters.

4. The number of engines on each stage should be maximized in size and minimized in number. It's true that a stage with multiple engines can sometimes make it into orbit if one of its engines shuts down prematurely, by running the remaining engines for longer. But a multiple-engine stage is also more likely to have a catastrophic (explosive) failure than one with just a few big engines, simply because it's more complex -- and, for the same reason, it will cost much more to design and manufacture.

5. The first stage of the booster probably can, and thus should, be economically reused -- not by flying it back to a runway with wings (which, as mentioned, will hugely decrease its payload and increase its cost), but by parachuting it into the ocean. "Waterproofing a [liquid-fueled and] pressure-fed rocket is extremely simple, as has been demonstrated for a number of prior launch concepts...

   "The cost of such waterproofing was always trivial. Exposure of a launch vehicle to salt water is only for short durations. Ships and naval aircraft...are exposed for very long periods to both salt water and salt air. They have somewhat higher maintenance costs, but they do not dissolve. Salt water is not a universal solvent."

Let's assume, however, that NASA decides to save development money on its next really big post-Shuttle launch vehicle by basing it as much as possible on the systems designed and manufactured for the Shuttle, rather than having to cook up something entirely new.

A "Shuttle-C" proposal has been floating around for almost two decades, undergoing repeated NASA studies without ever actually getting funded.

A Shuttle C would continue to use the Shuttle's solid boosters and external tank, and also its liquid-fueled engines -- but this time the latter would be in a small, separate module, which would reenter from orbit and land by parachute for reuse.

Sitting on top of this "SSME module" -- instead of the body of a Shuttle itself -- would be a big, cylindrical shroud containing all the payloads to be lofted into orbit, perhaps including a manned vehicle (like the OSP) at the top of the stack.

Depending on whether the engine module contained two or three SSMEs, Shuttle-C could boost 45,000 or 77,000 kg of payload into orbit, as against a mere 22,000 kg for the Shuttle -- and at considerably lower cost, given the lack of need for maintenance for any Shuttle Orbiter.

Alternatively, the engine module could be put underneath the external tank, and the payload perched on top of it, producing a more orthodox-looking rocket with about 5500 kg additional savings in total structural weight.

That payload would be big enough to carry a sizable capsule-based manned orbital ship with as much internal space as the Shuttle cabin -- plus an escape rocket and (if need be) a shroud, ejectable in orbit, to protect the capsule's heat shield from debris falling off the external tank and from orbiting space garbage -- with a large amount of additional payload capacity that could be launched at the same time.

And that additional payload could consist of an additional habitable (and separately recoverable) orbiting lab for microgravity and biology experiments, which the manned ship could dock with nose-to-nose after they had entered orbit (like the Apollo CSM and LM).

Alternatively, it could consist of an open rack of experiments -- or a "workbench" complete with manipulator arm to allow the craft to rendezvous with and repair satellites in orbit - which might lower the cost enough to make in-orbit satellite repairs economical in certain situations.

Other boosters have been proposed with a similar payload capacity -- such as a "Titan 5" which a 1988 Office of Technology Assessment study concluded might well be more cost-effective than Shuttle-C.

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only