tag:blogger.com,1999:blog-7598615455712402973.post7385804755262147257..comments2024-03-25T11:14:45.840-04:00Comments on Polymath: A SpaceX Heavy Lift Methane Rocket.Robert Clarkhttp://www.blogger.com/profile/16114043697010364282noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-7598615455712402973.post-40289360621684184722015-06-15T15:32:08.418-04:002015-06-15T15:32:08.418-04:00"If you replace the Merlins with a single Rap..."If you replace the Merlins with a single Raptor size to the appropriate thrust. You lose re-usability."<br /><br />Well, if you're re-designing the rocket anyway, how about using two or three much smaller engines burning methane/LOX? <br /><br />You could even use a "top lift" configuration, with the engines above the rocket body, much as the Apollo escape rockets were above the Apollo capsule. This would improve stability, as well as minimizing landing pad damage.Reggiehttps://www.blogger.com/profile/17478546089651522517noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-19028664149747739562014-07-07T14:36:57.621-04:002014-07-07T14:36:57.621-04:00While a 9 engine Falcon 9 seems unnecessarily comp...While a 9 engine Falcon 9 seems unnecessarily complex, it is also a configuration that is necessary for re-usability. If the 9 Merlin 1D engines are replaced by a single engine of similar thrust the rocket will never be re-usable in the fashion SpaceX is striving for -- namely vertical launch, boost back and vertical landing.<br /><br />It comes down to the fact that a hydrocarbon booster core will have a fuel fraction of about 90~95%. This means that of the lift off weight of the booster core 90~95% is propellant mass, the remaining is the weight of the structure, engine(s) and everything else. In order to propulsively land it the booster you need to be able to throttle down to about 5~7% of the lift-off thrust or roughly the weight of the empty rocket. It is difficult enough to make a rocket engine throttle between 60% and 105% the rated thrust. It is darn near impossible to run an engine at about 5% the rated thrust. The only reason SpaceX is able to play around with the Grasshopper and/or propulsively soft landing their falcon 9 boosters is because they have nine engines! This allows them to shut down 8 of them. Throttling the remaining to about 60% allows them to produce thrust equivalent to or slightly less than the mass of the empty stage.<br /><br />If you replace the Merlins with a single Raptor size to the appropriate thrust. You lose re-usability.dwight looihttps://www.blogger.com/profile/07724167433766696375noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-49257266896209329112014-04-02T06:24:30.114-04:002014-04-02T06:24:30.114-04:00Great blog ! Thanks for sharing! This page was ver...Great blog ! Thanks for sharing! This page was very informative and I enjoyed it. <a href="http://www.wheelcare.ie/about/garage-equipment/vehicle-lifts/" rel="nofollow">car ramps</a>.Anonymoushttps://www.blogger.com/profile/17930636396474114946noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-47751331997771982014-02-02T15:15:59.488-05:002014-02-02T15:15:59.488-05:00Hello Bob thank you for posting this.
It would be...Hello Bob thank you for posting this. <br />It would be interesting to see what this rocket would look like with 2 falcon nine cores as strap on boosters. I think this would be a more likely avenue for Space on its way to triple full sized cores. Teslamodelxhttps://www.blogger.com/profile/16689417009866626973noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-52081946687940181852013-11-20T01:43:01.984-05:002013-11-20T01:43:01.984-05:00Thanks for that. The lowered Isp 360 s is reasonab... Thanks for that. The lowered Isp 360 s is reasonable if you don't use altitude compensation on the first stage. However I do think altitude compensation is doable in the near term.<br /> But check your calculation again for the TSTO. It should be a lower payload than what I got when you take the first stage Isp as 360 s, not higher.<br /><br /> Bob ClarkRobert Clarkhttps://www.blogger.com/profile/16114043697010364282noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-52829326143503368092013-11-19T15:25:03.568-05:002013-11-19T15:25:03.568-05:00The same calculator gives me payload of 27541 for ...The same calculator gives me payload of 27541 for the SSTO case<br />(when not rounding anything, and using 360 sec isp for first stage)<br /><br />and 80694 kg for TSTO, 380 sec isp for second stage (vacuum optimized nozzle)Heikkihttps://www.blogger.com/profile/17832739911276147059noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-31612013254272575892013-11-01T13:25:15.665-04:002013-11-01T13:25:15.665-04:00XCOR reports a successful first hot-fire test of t...XCOR reports a successful first hot-fire test of their LOX-LH2 engine in the RL-10 class. I believe it is also piston-pumped, not turbopumped. There's several "firsts" there. <br /><br />GW<br /><br />Gary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-33520249613636343872013-10-31T21:04:45.370-04:002013-10-31T21:04:45.370-04:00 Thanks for the inside info on the XCOR hydrogen e... Thanks for the inside info on the XCOR hydrogen engine. <br /><br /> Bob ClarkRobert Clarkhttps://www.blogger.com/profile/16114043697010364282noreply@blogger.comtag:blogger.com,1999:blog-7598615455712402973.post-3991091610773248782013-10-31T17:36:09.169-04:002013-10-31T17:36:09.169-04:00Interesting results, Bob. We'll have to see ...Interesting results, Bob. We'll have to see about 27 engines, but 9 seems to be working very reliably on Falcon-9. <br /><br />I'm surprised SpaceX is not testing Raptor at McGregor, unless there is too much schedule interference in their two thrust stand facilities to accommodate it all. The bigger stand was built with noise reduction as part of the requirements. That's the Falcon-Heavy stand, which is supposed to be no louder testing at 4 million pounds of thrust than Falcon-9 was at 1.3 million on the other tower stand. <br /><br />They have Raptor plus Falcon Heavy plus all the verification tests for flying Falcon-9 hardware. That's a lot of activity and a lot of stand-occupation time. And that's why I think it might trace to scheduling. <br /><br />Odd that the article you linked says no one else has a LOX-methane engine. I happen to know XCOR Aerospace has one, and it uses piston-pump feed, not turbopumps. <br /><br />And you might find this tidbit very interesting indeed: I double-checked with my contact at XCOR. They have reached hot-fire testing with their piston-pumped LOX-LH2 engine, which is sized to replace the RL-10's on Centaur, including growth to double-the-thrust. ULA is bankrolling this one. <br /><br />GW<br /><br />Gary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.com