Transterrestrial Musings

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Look Ma, No Pilot!

[Warning, long space policy post]

That seems to be NASA's current attitude, and just one more reason that the Space Launch Initiative program should be hauled up to the top of the Vehicle Assembly Building at the Cape and hurled off the roof.

They're proposing (as was the case with X-33) that the new launch system be designed to be flown unpiloted, and have a separate, separable crew module when it has to carry people.

This notion of manned vs. unmanned launchers contains many myths. Even people who are supposedly expert often don't quite understand the issues involved.

One of those myths goes back to the Challenger disaster. Prior to it, Shuttle had been taking up commercial satellite payloads, as part of NASA's efforts to get the flight rate up, and thus reduce their per-flight costs. This had the incidental effect of severely damaging, and in fact almost destroying, the nascent commercial launch industry at the time, since the private developers were competing with a government-subsidized system.

After the Challenger disaster, an edict was laid down that Shuttle would no longer fly commercial payloads. As is usually the case when the government does the right thing (banning commercial payloads which were injuring the commercial launch industry), it was for entirely the wrong reason. The rationale was, instead, that "never again should our brave astronauts risk their lives doing things for which they're not required" (launching satellites).

The thinking here is that since commercial satellites can be launched on unmanned launchers, they should be launched on unmanned launchers. Never mind the fact that Shuttle launches are rarely single purpose, or that the costs may be lower (though in fact they weren't really--only the price was). At the heart of this thinking, of course, is the notion that spaceflight is dangerous, and intrinsically so. So since any human spaceflight is risky, we should restrict it to those purposes for which it is required that humans be aboard.

This would be a reasonable enough position, if it were true that a) spaceflight is inherently dangerous and that b) having humans aboard doesn't increase the probability of a successful mission.

Now for Shuttle, both of those assumptions may be valid, though for assumption (b) there were a number of cases in which crew checkout of the satellites prior to deployment might have been the difference between success and failure, even more so if the mission were designed with this capability in mind.

But there's no reason to think that it will be true for any future space transport.

Despite this, as always, the generals are fighting the last war, and NASA thinks that one of the problems with the Shuttle was that it was designed to fly crew on every flight, and are thus incorporating that "lesson" into the SLI program--by designing it to be capable of unmanned operation.

There is another factor that drives this decision. It's called "man rating." This is a concept that everyone who is familiar with space programs thinks they understand, and that very few, in fact, do. The myth here is that vehicles designed to carry people are intrinsically more expensive to design, build and operate, because they are "man rated." Now in the case of the next-generation Shuttle envisioned by NASA, even without a crew, the vehicle will still have to be "man rated," because it's meant to carry passengers in a separate module in the payload bay, so they won't get the cost savings that conventional thinking would indicate by not "man rating" it.

But the very notion that a space transport, even one that carries pilots and passengers must be "man rated", or that it will cost more than one that doesn't carry crew or passengers, is yet another myth.

To understand why, it's necessary to understand what man rating really means, and why it's therefore inapplicable to the new launch systems envisioned. And in fact, here's a shocking bit of news, to people who don't fully understand the concept--the Shuttle is not man rated.

A couple of years ago, I posted the following contribution (with some minor edits) to an FAQ over on sci.space.policy, which set off a rousing two-hundred-plus post thread/debate, but not one that ultimately changed my basic thesis.

Q: What is man rating, and what are its implications for the cost of designing, manufacturing, and operating a launch vehicle?

A: Man rating is a process by which design and operations of an expendable launch vehicle are analyzed and, if necessary, changed to reduce the chances of injuring or killing any person who might use it for transportation, relative to its design and operations prior to such analysis and modification.

It evolved as a practice in the 1960s, when, in our hurry to get to the Moon, we used existing ballistic missiles as the basis for our launch systems, rather than develop new space transportation systems from scratch (the Saturn was an exception to this).

The premise was that because these systems were designed to be used only once, and would be used en masse and redundantly (to lob warheads at folks to kill them and break their stuff), their individual reliability was sacrificed to a degree, in the interests of globally minimizing the overall cost. The reliability of the individual launch systems that resulted from this philosophy was deemed unsatisfactory for putting people on top of them (even for the early astronauts, who were test pilots at Muroc and Pax River, and riding on top of a tested guided missile was probably the safest thing that they'd ever done in their interesting careers).

Without getting into detail, it involved improving the reliability of the missile by using higher-quality components, adding in redundancy and testing in critical subsystems, getting lots of signatures, and ensuring that there were ways for the astronaut to semi-safely abort from a launch gone bad (in the words of Mitchell Burnside-Clapp, President of Pioneer Rocketplane--"attempted suicide to avoid certain death").

What does it not mean? It does not mean having systems/subsystems that permit people to be carried on board, such as cockpits, and life support. A man-rated Titan remains man-rated without the Gemini capsule that goes on top of it.

It also does not mean federal certification of a vehicle to allow it to legally carry passengers, which is more about testing and paperwork than about vehicle design per se.

This tradition continued into the development of the Shuttle in terms of design philosophy, though because large portions of the system were reusable, it started to lose some of its meaning.

The Orbiter itself is fully reusable (albeit with high maintenance costs--some would characterize it as "rebuildable" rather than reusable). And in fact, I am going to surprise (some) people here and say something good about the Shuttle, or, at least about the Orbiter.

It is a damned reliable vehicle.

It has never had or caused a catastophic failure. It has rarely caused a mission failure, most of which are caused by failures of the payloads themselves. In fact, perhaps someone can correct me, but I cannot think of a single instance in which a mission failed because of an Orbiter system/subsystem (other than vague recollections of some being somewhat shortened due to fuel cell or APU or similar problems). The one case where we had an on-board propulsion problem was caused by a faulty sensor, and the vehicle still made orbit.

The single event where we lost an Orbiter was due not to the Orbiter, but to one of the semi-reusable ballistic missiles that we had attached to it. Thus, I don't count it against Orbiter reliability.

In that spate of delays where the system was shut down in the late 1980's and early 1990's for hydrogen leaks, this was again a feature of the fact that we were crossfeeding from an expendable system--it had little or nothing to do with the Orbiter design per se.

Shuttle should thus give us great confidence that fully-reusable space transports can indeed be quite reliable. In fact, based on its performance to date, it should be clear that reliability is not the issue for a reusable launch system, as long as we have adequate performance margins. The only issue is cost of operations and turnaround, which cannot be addressed with the existing Orbiter--they will require a clean-sheet design.

For all this reliability, each Orbiter cost on the order of two billion dollars, and now would require several years of time to replace (with additional billions for reclimbing the learning curve and retooling). We only have four of them, and they are *all* needed to keep to scheduled plans.

Now for a thought experiment for those who are worried about "man rating" space transports. Ignoring the crew module (which as I said, is not relevant to whether or not the Shuttle is "man rated"), I challenge anyone to tell me how the Orbiter would be designed or manufactured differently, in terms of reliability or capability to deliver payloads, if it didn't carry crew on board.

[End Usenet excerpt]

My point is that a reusable vehicle represents a significant asset in itself, and that it has to be reliable, regardless of whether it has a crew, and regardless of the value of its payload, even human payloads.

Now, as I said, this is a secondary issue in the case of the intended output of the SLI program, because it's meant to be a Shuttle replacement, and must of necessity be capable of carrying people.

But I will argue that, for a space transport, a piloted vehicle will be lower cost, and more reliable, than an unpiloted one. Were it otherwise, Fedex would automate their aircraft and remove the crew.

There are a couple reasons for this. When things go bad, there are some situations in which having a pilot on board will allow the vehicle to be saved. It's often argued that this could be done remotely, but there's nothing like being on the scene, and feeling what's happening, to control a vehicle. Also, a remotely-piloted vehicle is vulnerable to a communications loss in a way that a piloted vehicle is not.

But the most important reason is that the ability to get FAA approval for flights of such a vehicle will go much more smoothly if the flight testing, and flight operations, are performed in a regime with which the regulators are familiar--i.e., piloted aircraft.

There were two potential development paths for space transportation. One was to take existing aircraft, put rocket engines on them, and gradually expand their performance envelope to the point at which they were capable of routinely flying into space. This was, in fact the evolutionary path that we were on in the late 1950s and early 1960s.

However, in our rush to beat the Soviets to the Moon, we short circuited this path, and in fact, cut it off altogether with the end of the X-15 program. Instead, we put men on top of munitions, because they were available, we knew how to build them, and we could do it quickly. As a result, all government-funded launch vehicle development (including Shuttle), has been right down the groove worn originally by Apollo and the early military and NASA unmanned space programs, and we seem to have trouble getting out of it.

The next generation of launch vehicles will arise from the first evolutionary path, which is being picked up again by companies like XCOR, and Pioneer Rocketplane, and some of the X-Prize contenders. NASA and its conventional contractors are institutionally incapable of following such a path--there's far too much bureaucratic inertia, and this bizarre notion of building an unpiloted reusable vehicle is just more evidence of that.

Posted by Rand Simberg at May 04, 2002 05:05 PM