I think modular, mass produced self-contained thrusters that can be clustered together in multiple stages should be the way to go. Also, having many of them on a vehicle reduces the risk of mission failure.Surely not the most efficient way in use of materials, but if production and quality control can be automated it would decrease the cost tremendously.Before you think I'm some genius, I wasn't the first with this idea http://www.astronautix.com/lvs/otrag.htm
I've been trying to understand what the most economical methods for shuttling people to LEO would be using technology currently available or at least available in the near future. Obviously reusability with minimal refurbishment and prep requirements would go the furthest. Next on the list would probably be simplification of the rocket itself in order to lower the initial cost of the machine (assuming it wasn't absurdly high in the first place, which would negate the benefit of reusability), followed by reduced fuel costs. The first two seem well under way by the likes of SpaceX, and apparently Blue Origin. Maybe they both still have room to simplify? Seems unlikely.
The real lowest cost way to shuttle people to orbit will be found when there is a) Multiple ways to do it. b) Multiple vendors of those systems, ideally supply multiple operators of those systemsc) No restriction on which vendor you use.
There first has to be a good reason for people to go into space before that happens
There are plenty of good reasons for people to go into space, just not ones you agree with.
Quote from: john smith 19 on 05/09/2015 11:44 amThe real lowest cost way to shuttle people to orbit will be found when there is a) Multiple ways to do it. b) Multiple vendors of those systems, ideally supply multiple operators of those systemsc) No restriction on which vendor you use. There first has to be a good reason for people to go into space before that happens
Quote from: Jim on 05/09/2015 12:17 pmThere first has to be a good reason for people to go into space before that happensThere are plenty of good reasons for people to go into space, just not ones you agree with.
Quote from: Borklund on 05/09/2015 11:55 pmThere are plenty of good reasons for people to go into space, just not ones you agree with.Quite wrong. There are few to none good reasons that are economical viable, which is needed to make it sustainable.
Needs are just wants felt more immediately - probably Mises.
Folks, the thread ASSUMES there IS a "good reason" for getting people into LEO in numbers, it is in fact the usual "chicken/egg" issue in fact at the moment but we're assuming the need is there.
Back to the OP again, there is really a need to define some parameters on the "market" to be able to define the "best" method. For example, if your yearly "market" is 100 people to orbit (very early projections for a LEO tourism market with a much lower but still pretty high price) then having a vehicle capable of putting more than about 9 people per month is a waste. Further if your market consists of 100 people a month (very difficult to justify at this point) but they are divided between several destinations (say 4, 25 passengers each) then having a vehicle capable of putting 100 people per flight into orbit is not a good solution.
The Rutan Quickie was marketed as a 1-place $4,000 (1979, so ~$13k now) aircraft, capable of around 100MPG with an 18hp engine (could probably do better with a more efficient modern engine, especially diesel). According to the following blog post (https://blogs.law.harvard.edu/philg/2007/03/19/airbus-a380-more-fuel-efficient-than-a-toyota-prius/), a loaded, all economy seating A380 with 850 passengers gets similar fuel economy. It would require 850 Quickies to carry the same amount of passengers as a single A380, but it would do so at a price of roughly $11M, compared to the ~$430M for the A380. Granted, the A380 is a far more capable aircraft all around (except its runway requirements, heh). Now, it wouldn't be practical to replace all airliners with quickies, if for no other reason than the sheer amount would congest the runways (but in terms of space access, we're so far away from having that problem). But lets just say we could, mass manufacturing would bring the unit as well as parts cost down further, so we'd get even more passenger transport capabilities for the money. Maintenance could be standardized and tasks such as structures inspection could probably be largely automated (imagine an automatic car-wash, but with X-rays and sophisticated data processing software, etc.), which are things you can't do when you only have a few thousand (MASSIVE) units spread around the globe. Ok, that's enough of the apples to carrots to pork chops comparison.
This is a key point. What is the "shape" of the market?
As for the market size, I guess it's not fair to say "unlimited", while at the same time using current-day figures is boring for the sake of discussion. One of the big points I was trying to make is how to reduce costs to the point where the pricing enables a larger customer base (even if the customers are wealthy by most standards) over current options. Lets just say the market is big enough to justify the development costs of RLVs. Realistically speaking, SpaceX is in the best position as they have one LV which they could use for passengers, cagro, and satellite payloads, thus spreading the NRE for the core rocket tech as much as possible. But that doesn't make a fun discussion, does it?
Thanks Randy for thought-provoking response and keeping to the topic of the OP.
I must admit that it is a bit silly to consider practical, near-term solutions to a hypothetical situation which is unlikely to come to fruition any time soon. And at any rate, any "practical" solutions depend on so many factors, with at least a handful of them brought up in this thread already. I think that makes the topic that much more interesting.
What I'm still not entirely convinced of is that a larger LV capable of carrying more passengers is more efficient overall than smaller ones, even if there's enough passengers to justify its size. Though I admit the issue brought up earlier in this thread with docking so many spacecraft to a space station is one of the best arguments against it.I'm going to further argue in favor of smaller & cheaper LVs, and while I know it's a stretch to apply the following to this topic, I still want to entertain this thought:
The more I think about it, the more I like the jet-powered LAP concept. As you point out, it should be much simpler (and thus cheaper) to develop than a specially designed aircraft. Even if we could use an existing aircraft, the performance would be much lower than what is possible for a LAP. For one, the speed and altitude could be greatly increased over the flight regime jet engines are typically suited for via LOX/water injection (perhaps around Space Shuttle staging velocity and altitude?). The simpler structure should also make aerodynamic heating more easily managed than a full-on airplane of comparable performance.
(some snippage)You could have more cross range or build it so that it can land at an airport (ideally in a state that allows it's self ferry back to base). You'll probably want either more cross range or > 24 hr endurance so the launch site comes back under its orbital track without requiring enormously high cross range. BTW one interesting calculation you can do on a spreadsheet is to run the rocket equation with different levels of Isp and partial delta V's and losses to orbit. High Isp (relative to a rocket) means you have a structure which is much heavier than any known rocket, but only air breathers give 1000's of seconds of Isp. Once your breathing air winged lift lets you lift mass 3x take off thrust, although the Launch Assist Platform with afterburning and inlet fluid (either LOX or water) injection can give you a (relatively) simple 1st stage structure with high thrust at ground level and maximum payload (exactly where you need it) while sustaining acceleration up to maybe M4 without exotic technology like SCRamjets. The improvement on the available mass fraction for structure is quite remarkable.
Your just missing a couple of small details in your comparison.
On the one hand you're saying "What's the smallest you can make it?" and on the other you're saying "What's the most economical you can build?"
High Isp (relative to a rocket) means you have a structure which is much heavier than any known rocket
How do you figure? I don't see why that would inherently be the case.
Seriously a number would help msat
SpaceX and CST100 are both 7 "people" as payload, call one of them a "pilot" and round down that's 6. Currently they can't launch but every couple of months and there's only one "destination" which is the ISS.So we could "assume" a scenario based on 8 people per month, 96 a year but that 'technically' wouldn't even strain the system we have assuming we get a third provider. I also don't think it would help lower costs all that much. Anyone have suggestions for a "conservative" number?
Your on the NSF-forums, "speculation" is a way of life around here However your correct we DO have to define the problem and parameters if we're going to keep going which is what I'd like to see happen.
Your "Quickie" analogy breaks down hard, even before the issues of range and speed: How many passengers on an A380 can fly a "Quickie" let alone the A380 they are on? So as JS19 points out you have to have an automated flight systems which would NOT be cheap nor easy to install in a "Quickie" and you'd have to (in the example) build, test, install, and test 850 of them.
Lets talk a bit more relevant one:7 Falcon-1s versus 1 Falcon-9 with Crew-Dragon.Using the numbers from the following site (for reference ONLY people ):http://www.spacelaunchreport.com/falcon.htmlF-1e would put 1mT (1000kg/2205lb) so lets "assume" for a moment that we could make a single person, automated spacecraft reentry vehicle AND fit a person and some "supplies" inside it and launch it on the F-1e. The cost to do so quoted on the above site is $9.1 million dollars. SpaceX quotes a Falcon-9 launch at $61.2 million, so at its most basic the Falcon-1 option costs at least $63.7 million while the single Falcon-9 only costs $61.2 million. F9 is $2.5 million less than multiple F1es. (And this is before the added costs of developing and building the automated one-person capsules for the F1e)Now you can still argue that multiple "smaller" launches more often does in fact make more economic sense in some cases and it does. But in general I don't see it being economical for personnel launch without some sort of "infrastructure system" in place (such as the suggested launch loop or skyhook/rotovator, etc) where you are transferring people constantly. Even then I doubt single person vehicles will be cost effective.(Of course someone WILL argue differently and one such person is Danni Eder who originally came up with the jet-LAP assisted launch concept at Boeing who has a google book he's working on here: http://en.wikibooks.org/wiki/Space_Transport_and_Engineering_Methodshttp://en.wikibooks.org/wiki/Space_Transport_and_Engineering_Methods/Human_TransportWhere he argues the case for single person transports)
If you haven't yet I'd recommend taking a read of these threads:http://forum.nasaspaceflight.com/index.php?topic=29160.0http://forum.nasaspaceflight.com/index.php?topic=26680.0;allhttp://forum.nasaspaceflight.com/index.php?topic=25095.0;allAnd I'll jump on the most "obvious" flaw before anyone else does: If your rocket stages are your main turn around driver then having a stage that you CAN actually turn around faster doesn't help you. ... Unless you have multiple rocket stage sets waiting for launch that is