guest blogger john hare
It is a requirement of living that you make assumptions about things. If you have to have all conceivable information on any subject, and have all of it verified to a high degree, before you do anything, you will never do anything. You have to assume you will get paid for the work you do, or not do it. You have to assume your vehicle won’t suddenly explode on the way to work, or don’t go.
In almost anything to do with spaceflight, we have to make assumptions based on less information than in most of the rest of our daily lives. This is because the accurate information is just not there. Is there a market for space tourism? Probably. Is it big enough to support a few companies? Probably. Will the first fatality kill the industry? Probably not. Is helium three worth going after on the Lunar surface? Depends on a dozen factors, I’d say not now.
All these assumptions are best guesses based on the best information available. Of course the best guesses themselves are based on your personal viewpoint. It is safe to assume that Marks’ assumptions are almost opposite Rands’ for instance.
What got me thinking about it this time was a comment by ‘the other Bob’ at Rands place. He was concerned that the existence of propellant depots might somehow prevent the development of better in space propulsion systems. I can barely follow the logic of this. If gas stations (propellant depots) exist, there will be no market for electric and hybrid (ion, tether, and laser) vehicles, or incentive to develop them. The way I see it, even if launch prices drop to $500lb, every ton of propellant you don’t have to buy is a megabuck of savings.
The assumption seems to be that if you have a boat load of bucks invested in depots, you don’t want to do anything to make that investment worthless. My assumption is that if Hareball Aerospace has a nifty propellantless drive, Masten Orbital Refuelers is on their own. In a free market with multiple aggressive players, somebody is going to use anything useful for competitive advantage. Bobs’ assumption seems to be that one player is going to dominate space for the foreseeable future. Mine is there will be many. Differing assumptions based on the apparently the same information give very different answers.
The recent airbreathing vs rocket discussions have some underlying assumptions that may not be obvious at first glance. One assumption I’ve not seen stated exactly is that you must develop both systems yourself. On that assumption, rockets will win almost every time. It is easier to set up a shop to develop two rocket engines for the two stages than a turborocket plus a rocket for the upper stage. If you have to develop both simultaneously, I’d say build a large rocket for the first stage and a smaller one based on the same tech for the second.
If however, a mach 4 turborocket system is available COTS, then the assumptions change fast. If first stage propulsion development consists of a check to the order of Bossards Turbospeedy Engines, years of development time and a lot of uncertainty just left the building. I would bet that XCOR would even have looked at this for the Lynx if it had been available substantially before airframe work started.
Another annoying assumption by some is that Isp is everything. Laser/hydrogen is the wave of the future because Isp is 50% higher than the best that chemical rockets can do. Scamjets are the wave of the future because they will reach mach 20 without onboard oxygen. And so on. My assumption is that choosing a launch system based on Isp alone is like choosing a wife based on bra size alone, the superficial attraction occasionally hides a really nasty disposition.
One of my personal assumptions is that turbopumps are not that tough, if done right. Most knowledgeable people will disagree with this. People in the business have limited budgets and developing a pump system adds another whole set of problems as if they didn’t have enough already. I assume that the increased engine performance will reduce problems in other areas to the point that the pumps pay for themselves during development even before the vehicle flies. I make the assumption that 30psi fittings will be easier than 300 psi fittings.
Perhaps the most important assumption most of us make is that space is worth doing and will be profitable. There are many with the opposite assumptions though, and they can’t be dismissed out of hand. One of the most important things we can all do is find ways of altering the base assumptions of those that are both interested in space, and have a negative attitude toward the profit potential. Not with words alone though, we need proofs that will be accepted by the ones we need to help us. Why we want to go must be answered, and it must be answered with integrity.