Endeavor's Passing

I never got to see any of the Shuttles during their active service as spacecraft. Planned West Coast military launches from Vandenberg were scrubbed after the Challenger loss. I did hear the double sonic boom a couple of times  when Shuttles crossed the coast en route to landings at Edwards AFB.

And only by sheerest luck did I end up seeing Endeavor on its final piggyback flight last week: Paula happened to turn on local TV news half an hour or so before it overflew San Francisco en route to retirement in Southern California.

It was an impressive sight. But like the sight of USS Iowa passing under the same bridge, it was a somewhat melancholy occasion. What in my early adulthood was the spaceship of the future has become a spaceship of the past.

Will we see its like again?


The Shuttle program was star-crossed in multiple ways. Thus its experience does not provide a 'fair' test of reusable spacecraft. This is the good news.

First of all, it conflated the roles of experimental prototype and operational vehicle: a beta pushed into production. Its development costs were squeezed, compromising the design, and further compromised by demanding of it an enormous payload capacity.

Given all these fundamental shortcomings it is remarkable that it succeeded at all. It surely cost far more to operate over its service career than either a capsule atop a conventional rocket or a smaller, fully reusable spacecraft, refined from a prototype, would have cost - not to mention the greatest and most needless cost, two large crews. Spaceflight is dangerous, but the points of failure for both Challenger and Columbia were direct results of the flawed development process.

We cannot say how much a more robust Shuttle would have cost to operate, or how safe it would have been. All we can say is that it would have been cheaper and safer than the ones we actually flew.


Unfortunately, we can also say that a more robust Shuttle would have been - would still be - horrendously expensive to develop. The projected development cost of the original Shuttle design, circa 1969 - before the compromises mentioned above - was on order of $10 billion. This is equivalent to $60 billion in present-day dollars. Hear the deafening sound of wallets snapping shut.

And it gets worse. Assume a 30-year service lifetime, with monthly launches - less than hoped for, but a lot more human spaceflights than we have actually flown. The apportioned development cost - ignoring interest and such - thus comes to about $170 million per mission. Remember, this does not include any of the costs of actually flying the missions, or training the astronauts, or anything else: It is just the development cost leading up to the first operational flight.


There is also a line of argument, all too credible, that a truly viable reusable spacecraft - one that is cheaper in the long run than expendable rockets - is just not attainable at our techlevel. We know a lot about building large, lightweight structures, along with powerful engines able to drive them into the upper atmosphere or even into space. We can do significantly better at these things now than we could fifty years ago, but not dramatically better - an indication that our technology in these areas is pretty mature.

But getting into space is so intrinsically difficult that our normal technique involves large, expendable boosters or lower stages. Payloads are, at most, a few percent of launch weight. And the problem for reusable spacecraft is that they must carry heavy fittings, such as heat shields, along with wings and landing gear, that their expendable counterparts can do without.

A simple design burdened with these heavy fittings probably couldn't reach orbit at all. But a design refined to the point that it can reach orbit is liable to be so extreme in its specifications that it requires extensive  tear-down and inspection, and perhaps refurbishment, after every flight. Which defeats the whole point of being 'reusable.'


In all of this there is a glimmer of hope: We are not dealing here with 'cold equations' but with devils in the details, and the lines between not-quite-feasible and just-feasible are pretty fine. And even as the Shuttle rode off into the west, the US has begun operating another spaceplane, the X-37B.

This is in no sense a 'Shuttle replacement.' It is very much smaller, launched atop a conventional expendable rocket, and it is unmanned. It is also a classified DARPA project - even thought it began as a NASA project - meaning that not much is being said either about its performance or its missions. But it may well be more operationally robust than the Shuttle - in particular, safer during re-entry.

Incremental progress in mature technologies is glacially slow compared to the Moore's Law-style progress seen in tech revolutions. But in the course of this century we might (or might not!) gradually develop our launch capabilities to a level approaching what the Shuttle once hoped to achieve.

After which, things could get interesting.


Discuss.




Note: A recent, truly awesome XKCD comic has a relevant comment on space rocketry. You will have to look ... carefully ... to find it.




Another Note: Unrelated to this post, but a blog reader has done the service of converting my Planetary Climate Sim into Linux and Win32 object code.

The sim itself is designed primarily to test the effects on an Earthlike planet's climate of greater orbital eccentricity or different axial tilt. It also has some settings for different average locations within the habitable zone, greenhouse gas composition, differing proportions of ocean and land surface, and so on. But these things are far more complex, and pretty much above my pay grade.

 I don't warranty the results! And I haven't tested the Linux and Win32 versions at all - let me know how they work! I'll pass any bug reports along to the contributor.




The image of Endeavor and its 747 carrier above the Golden Gate Bridge comes, a bit paradoxically, via the Baltimore Sun.