This week’s successful landing and recovery of a launch booster by SpaceX got a lot favorable coverage and was an impressive feat. But as a classically trained aeronautical engineer who spent more than three decades flying crewed rocket ships into space, I have always looked at the concept of a fly-back booster with skepticism.
The rocket equations tell us that it’s extremely costly, in terms of propellant, to get every ounce of payload into orbit, and that sizing the vehicle so that it has just enough propellant (and no more) is the most efficient way to do things from a physics standpoint. Carrying the extra fuel, structure and systems to fly the booster back to the launch site erodes that efficiency and seems like heresy to those of us who have struggled for years to get as much performance as we could out of every launch. With payload, the Space Shuttle Orbiter weighed about 250,000 pounds at launch and we spent many hours arguing over an extra 50 or 60 pounds before every flight. Margins were measured in hundreds of pounds–never more than a thousand. That’s a very tiny fraction of the total vehicle weight, because those pounds were important.
Yet here comes Elon Musk (and Jeff Bezos), flaunting the rocket equations and saying, “Hey, look at us; we can fly our first stages back to a safe landing.”Since they haven’t changed the laws of physics, is this just blatant exhibitionism or an excessive show of wealth, like the archetypal fat cats lighting their cigars with $100 bills? Sure, you can do it, but is it economical? Does it make sense? The truth is, from a pure physics standpoint, if your goal is to get as much payload to orbit as possible with every launch, the answer is no. But that’s a fairly “pure” goal, isn’t it? If your business is getting payload to orbit while making money, maybe bringing back the booster for refurbishment so that you don’t have to build one from scratch every time is worth a look.
I’m hardly an expert in how to make such a venture pay. I do recall one macroeconomics course back in college, but our aero professors considered any time we spent studying something other than wings to be a waste. But I can imagine that if you build and fly enough rockets, you might very well reach a point where flying a few extra flights with physical inefficiency could be made to pay if you could refurbish instead of build new each time. The trick will be, does the reusable booster lower launch costs enough to generate new business and can the booster be refurbished cost-efficiently? No one really knows this yet.
Even the Space Shuttle was originally imagined (and sold to Congress) with a first-stage fly-back booster; this not a concept new to SpaceX or Blue Origin.The Shuttle launcher was a winged, manned craft that would launch the Orbiter to the edge of the atmosphere, then return immediately and land on a runway at the launch site. The fly-back booster was shelved in the 1970s due to cost and complexity. The funding wasn’t sufficient to develop the necessary technological leaps and the disposable external tank and reusable booster rockets were developed in its place. Were the reusable solids economical in the long run? I really don’t know. The cost of refurbishment and processing was always amazing to me and I’m sure some bean counter somewhere could do a life cycle study of the program and figure that out. As another example, of course, Scaled Composites’ White Knight is effectively a fly-back first stage for SpaceShipOne, a non-orbital vehicle that still sniffs the edges of space.
Of course, if we ignore the physics and economics, we are still left with the question of why someone would spend the resources to develop such a system when it is likely that they can’t see the end of the tunnel regarding its profitability. Then again, doesn’t that define business risk? The Wright Brothers flew their first powered machine only four times before it was wrecked by a gust of wind. Hardly a cost-effective method of traveling the distances they achieved, considering that they also sold bicycles that were safer, faster and longer-lived.
Did the Wrights have a dream of a massive airline system, military planes changing the face of warfare and the idea of flight becoming a normal part of the human condition? From my readings, I don’t think so, at least not early on. They just wanted to solve the problem of flight. They wanted to fly. Aviation, and by extension spaceflight, has always been, to a degree, about the dream. Some dreams pay off handsomely in the end, others simply cost a lot of money, but leave a smile on the face and a warm spot in the soul when you’re done.
If you told me 20 years ago that someone would be successful with a fly-back first stage, I’d have quietly smirked a little. Possible, yes. Practical? Not a chance. But times change, missions evolve and technology advances. The dream of aerospace engineers since the late 1970s has been the X-wing fighter from Star Wars. You’d be surprised how many aeronautical engineers of my generation use that benchmark. Fly it off the ground into space, then fly it back and land–nothing thrown away, just gas it up and go again.
Now that it’s been done, maybe the next step can be achieved as well. I suspect that there is a very long way to go, and that the launch trajectory used is unusual and physically inefficient. But it worked and the history of human engineering is to refine and improve until the impossible becomes routine. The physics are only one part of the equation. How many of us fill all four seats in our cars driving to work every day? Most of us go solo, carrying all that extra mass on a round trip every time.
Wouldn’t it make more sense if we all rode motorcycles? From a physics standpoint, sure. But we like our creature comforts and it’s hard to drink a Starbucks on a bike. And isn’t it nice to be able to travel on our own schedule, and not have to wait for another member of a carpool who got stuck in a long meeting?
Other considerations than just pure physics are in play in most parts of our lives. Why not spaceflight as well? That 1903 Wright Flyer was completely and utterly impractical at first glance, but it took us places we could have never imagined. Let’s see where these new kids take us in the coming years. I might not want to invest my money in their programs right now, but then I’m risk-averse with my money. For those willing to put all their chips in play, the big gamble might well pay off. I hope so, because I still want my X-Wing fighter.
Paul Dye is editor of AVweb’s sister publication, KITPLANES and is a retired NASA Senior Flight Director who flew the Space Shuttle and International Space Station projects. He’s an accomplished amateur builder of aircraft.
