Path: utzoo!attcan!uunet!lll-winken!ames!pasteur!ucbvax!hplabs!hplabsb!dsmith From: dsmith@hplabsb.HP.COM (David Smith) Newsgroups: sci.space.shuttle Subject: Re: QUESTION: Shuttle round trips to the moon? Keywords: shuttle moon Message-ID: <5108@hplabsb.HP.COM> Date: 12 Jan 89 19:22:23 GMT References: <14549@oberon.USC.EDU> <1064@ns.UUCP> Reply-To: dsmith@hplabsb.UUCP (David Smith) Organization: Hewlett-Packard Labs, Palo Alto, CA Lines: 43 In article <1064@ns.UUCP> logajan@ns.UUCP (John Logajan x3118) writes: >> Can the shuttle fly to the moon? >No. Consider that the ultimate result of burning all that fuel (both liquid and >solid) is the final speed -- orbital speed of approximately 17000 mph, and >getting to the moon requires closer to 25000 mph. Thus the shuttle would have >to carry at least 1/4 again as much fuel as it does. Quite a significant >increase! It's worse than that. To start with, the 1/4 figure is too low. (25000-17000)/17000 = 1.47 > 1.25. (The ratio of excape to circular orbit velocity is actually sqrt(2).) Then you are nailed by the fact that the final speed gain of a rocket is the exhaust velocity times the *log* of the mass ratio. Let's take our favorite shuttle on a swing around the moon. That will take a delta-v of ~7200 mph. Isp of the SSMEs is 455 sec => exhaust velocity is 10,000 mph. So the mass ratio must be exp(7200/10000), or just over 2. That means propellant required is just a bit more than the weight of the orbiter plus its fuel tank -- around (probably over) 250,000 pounds. That is 4 times the used-to-be max quoted payload of the shuttle, so it would take four flights (4 times the fuel) to send one shuttle around the moon. Quite a significant increase! Actually, I expect that more than 64,000 pounds of fuel could be brought up at a time. Just send up shuttles with empty cargo bays. The fuel not burned on the non-cargo is greater than the would-be weight of the non-cargo, and the thrust-to-weight ratio is greater. And once safely in orbit, the performance margin fuel could be transferred. Or if we used high-end shuttle-C (i.e., the variant with 3 SSME's), it would take just one tanker flight. If we wish send a shuttle on a lunar orbit mission, we must tack on another 3000 mph each for lunar orbit insertion and trans-Earth injection burns. Then the mass ratio goes up to 3.7, and we need 675,000 lb. of fuel: ten tanker shuttles, or three shuttle-C's. Now we have to work out how to manage reentry, since the shuttle will come in with twice the kinetic energy of an orbital flight. -- David R. Smith, HP Labs dsmith@hplabs.hp.com (415) 857-7898