Paul Spudis says that propellant depots are a necessary but not sufficient condition for opening up the solar system.
Well, in the long run, sure. But as Clark Lindsey notes, in the short term, I think that a dollar spent on reducing launch costs will have a lot higher ROI than a dollar spent on getting propellant from the moon. That’s just the harsh economic reality, largely because reducing launch costs is a very low-hanging fruit, given how ridiculously and unnecessarily high they currently are. Elon has already started to show the way, and fully reusable space transports that develop out of the suborbital and other markets will accelerate the process. Once we solve that problem (and it won’t take that long, once we get serious about it, which will start when the markets flower), then ISRU will start to look a lot more attractive, because doing it will be a lot cheaper as well.
Are there any ‘cargo-only’ ideas that you think have significant merit? How high is a reasonable maximum g-force for a rocket that’s never going to carry crew or fragile cargo? (In fighters, at least, the g-tolerance of the plane itself has been well beyond that of the pilots since the eighties.)
Maybe launch cannons. But the payload is generally small unless you’re going to make a major infrastructure investment, so it would be very inefficient for propellant delivery.
No, I really believe that we’ll haul all cargo on “human rated” space transports, just as we haul all cargo on “human rated” land, air and sea transports. There really is nothing about spaceflight that puts it into some other ethereal realm in which it is unlike other forms of transportation, other than that (to date) it has been so rare.
I think the transport might be “human rated,” but not necessarily have human(s) on board. If you remove all the gadgetry needed to keep a human alive, you can increase payload, particularly for small vehicles. For instance, for delivery of consumables to a space station with low replacement cost, SpaceX could delete the launch abort motors and most of the propellant, giving larger payload. If a payload and Dragon is lost on one in 100 flights, the replacement cost of the Dragon and payload may be less than the increased revenue from the larger payloads on the other 99 flights… it should be analyzed in detail.
Yeah, but if deleting all the stuff you don’t need means splitting your production line in two, there is a good chance it aint worth it. That’s only if you are competing on price though, which I would recommend against. To many government-subsidized competitors out there. Really, the silver tuna is being able to mass-produce the product – which is not rockets, incidentally, it is tons to orbit. Once you get something nominally reusable, taking out the integrated LES system between flights makes as much sense as changing out a truck’s transmission between running an in-city and cross-country route.
Luckily, anything with a rocket is largely fuel anyway. So if you don’t need the LES for a flight, just don’t gas it up.
SpaceX would gas up the LES anyhow, since if it isn’t used during launch it gets used to cushion the landing.
Cargo flights might be a good way to build up a large number of successful flights prior to carrying people. This might enable a slightly faster and less analysis driven development program.
I often wonder about a launch prize of say $50m each to the first three groups to fly a hundred orbital flights, with say at least ten of them carrying people. Cargo flights might help with the learning curve and generating some revenue sooner. If the vehicles are cheap failure is more affordable.
As Doug said, small vehicles where pilot weight (and associated systems) would seriously cut into payload can favor cargo only flights, and I suspect it is at such small scale that RLV development needs to start. I suspect such vehicles will actually want to be able to fly with or without people.
A SSTO HLV approach where engine modules are returned by a smaller human carrying RLV is yet another cargo only launch vehicle possibility. The HLV would have no reentry capability by itself and the tanks would stay in orbit.
A couple of points: Part of the reason for the huge cost of space launches is the demand for near-perfect reliability in the launcher and (often) the payload. Comsats, for example, are hugely expensive because they have to operate for decades without attention. Of course, if there are people on board then a launcher very unlikely to blow up is a good idea.
However, what about the launching of cheap bulk items (structural girders and fuel, for example)? Surely it is acceptable to have 90% reliability for things like this rather than 99.9%, if the cost of the launch is halved thereby? And regarding the comsat issue – maybe they could be made less reliable and therefore cheaper, if we had some way of getting there to fix them if they go wrong?
yeah, John Hunter’s http://quicklaunchinc.com/ is the best bet for space cannons. We’ll see if his funding comes through.
@Fletcher-
Another related reason for the cost being so high is the very low flight rate. With higher flight rates, high enough to keep factories and crews proficient (crews only once reusability comes into play), cost will go down and reliability will go up.
john hunter’s “biggest gun in the world” concept struck me as wacky at first but on second thought might actually be the right kind of innovative thinking we need to reduce costs signficantly to launch. i think few are aware of his concept. i wonder, trent, how much he needs for prototype? any potential commercial contracts? maybe he should launch a wheel of cheese first and then SES will give him a satellite…
Airliners manage to get both high reliability and low cost by not throwing the aircraft away after a flight, or requiring an overhaul by an army of technicians between flights. Instead of a ground crew of hundreds occupied for weeks or longer on 1 launch, airliners have a ground crew of dozens managing several flights departing each day. When there is a malfunction, such as an engine out, the aircraft and payload are usually both recovered intact. The net result is the aircraft has thousands of flights to pay for itself with modest incremental costs for each flight.
I’ve been thinking more along the lines of horizontal takeoff – carrier style. (Or: Cannon, in slo-mo)
If one manages roughly 15g constant acceleration, it doesn’t take all that much track to rack up a sizable slice of delta v. You get the ‘fun’ of breaking the sound barrier while still on the ground, the track and ‘pult would have substantial costs. But just a few short miles of track would mean that there wouldn’t need to be much ‘lifting’ fuel at all – (it would all be delta v to manage a real orbit).
Al’s comment is not to be dismissed. I saw, at a recent conference, a presentation by one of the people who builds electromagnetic launchers for aircraft carriers (they are going into service). They’ve launched Mach 6 projectiles at White Sands…it’s very impressive.
Given that they know the engineering for the launch, I have no doubt that their scale-ups (mass-wise) are accurate. They have done mass scale-up analyzes which show a certain cost per initial vehicle mass at Mach 6, then extrapolate that to orbital insertion. I’d agree with the Mach 6 analysis. The orbital extrapolation gives a cost for LEO insertion of small payloads (100s of kg) into orbit for $2,000 per kg.
However, I’ve performed thousands (maybe tens of thousands) of trajectory analyzes which show that the energy-based trajectory guesses are really bad. I wouldn’t rely on analyzes which involve a shot from the earth’s surface to some hypersonic velocity, followed by rocket propulsion, unless the entire trajectory has been analyzed.
Theres some contorted logic here, like saying we need to open the Wild West so that a chain of gas stations and fast food outlets can be built.
Even a muzzle velocity of mach 6 is not going to help that much, especially as air drag is going to take most of that and the vehicle is going to have to be severely compromised to take those accelerations (15g requires a 15km launcher and vehicle structural mass is to first approximation proportional to peak acceleration) and to mitigate drag (will effectively require reentry shielding on a stream lined shape just to get to orbit). It is also likely severely scale limited, making the aero losses all that much greater.
In comparison air launching with a battery powered scaled up quadrotor effectively adds 1000-1500m/s of delta v at much lower up front and operating cost (very cheap and low risk) – and could do it most anywhere. The accelerations are low and the quadrotor can carry the vehicle internally so that the vehicle can be designed for near vacuum only with no aeroshield, aerodynamic compromises or tank insulation.
“However, what about the launching of cheap bulk items (structural girders and fuel, for example)? Surely it is acceptable to have 90% reliability for things like this rather than 99.9%, if the cost of the launch is halved thereby?”
Assuming it would get you as low as half, but reliability isn’t only about value of the payload, but also the certainty of delivery. Even ‘bulk’ items are very important, if the end user absolutely needs them ‘on time.’ Visualize a future conversation similar to this:
Launch provider: “We’re sorry your payload was lost during launch, but it was only water. We’ll give you a free launch in three weeks.”
Customer: “That ‘water’ was meant to be reaction mass for our gas-core NTR spacecraft that’s almost ready to go. I’m still paying people already up there, waiting to receive it, and do other preparations. You can’t get me another launch for three weeks, but my departure window closes in two…!”
I don’t pretend to have ever managed any kind of construction project, but I do know how important the timely arrival of bulk (or other) materials can be, especially if the ability to store them on site is limited. ‘Just in time’ operations are all about that.