Comments on: Orbital Access Methodologies Part III: Pop-up TSTO http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/ Random Musings from the Warped Minds of Jonathan Goff, Ken Murphy, John Hare, and Kirk Sorensen Thu, 02 Sep 2010 05:17:09 -0700 http://wordpress.org/?v=2.8.4 hourly 1 By: Anonymous http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2977 Anonymous Mon, 07 Jul 2008 12:41:00 +0000 http://selenianboondocks.com/?p=511#comment-2977 I agree, L/D drives the peak g's, but some sort of high drag device at initial reentry could reduce the peak heating even if it's done in a ballistic fashion. I agree, L/D drives the peak g’s, but some sort of high drag device at initial reentry could reduce the peak heating even if it’s done in a ballistic fashion.

]]> By: Jon Goff http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2969 Jon Goff Tue, 01 Jul 2008 14:24:00 +0000 http://selenianboondocks.com/?p=511#comment-2969 Ivan,<br/>I honestly don't know whether your idea would work or not. I think Henry Spencer has suggested such an idea at one point, so it isn't silly. I just don't have the tools to easily tell if it really makes sense. That said, I'm a fan of avoiding expendable elements, particularly ones that may be fairly expensive to replace like this. One thing to remember though, the g-loading on reentry is almost entirely dependent on L/D. So unless the parachute somehow gave you a high L/D, it wouldn't really affect the g-loading that much. Also, I wonder how effective it would be if the upper stage is far ahead of the parachutes (as is often the case). <br/><br/>Just some thoughts.<br/><br/>~Jon Ivan,
I honestly don’t know whether your idea would work or not. I think Henry Spencer has suggested such an idea at one point, so it isn’t silly. I just don’t have the tools to easily tell if it really makes sense. That said, I’m a fan of avoiding expendable elements, particularly ones that may be fairly expensive to replace like this. One thing to remember though, the g-loading on reentry is almost entirely dependent on L/D. So unless the parachute somehow gave you a high L/D, it wouldn’t really affect the g-loading that much. Also, I wonder how effective it would be if the upper stage is far ahead of the parachutes (as is often the case).

Just some thoughts.

~Jon

]]> By: Ivan Vuletich http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2968 Ivan Vuletich Tue, 01 Jul 2008 03:08:00 +0000 http://selenianboondocks.com/?p=511#comment-2968 Hi,<br/>Great series. One idea to help with the reentry TPS challenge that I've been kicking around is a sacrifical "reentry drag chute". <br/><br/>This would be some sort of parachute that you would deploy at the beginning of reentry and whose function is to provide extra drag as high as possible during rentry before buring up, thereby allowing a lighter & simpler main TPS.<br/><br/>In form it might look more like a solar sail than a conventional parachute. See <br/><br/>http://www.spacedaily.com/reports/NASA_To_Attempt_Historic_Solar_Sail_Deployment_999.html <br/>In that article they mention one of its uses would be to de-orbit LEO satelites.<br/><br/>Alternatively maybe a fine mesh of stands of an ablative material might work better.<br/><br/>If it works as advertised it could make for an easier TPS problem, reduce g loads on re-entry and help maintain the proper orientation on reentry. It might be able to help with some about cases as well.<br/><br/>Its also something that could be tested with sub-orbital vehicles :-)<br/><br/>Key challenges would be to:<br/><br/>1) Getting enough usable drag before it burnt up.<br/><br/>2) Getting it deployed and keep it deployed in near vaccuum conditions as it would need a lot of surface area to be usefull.<br/><br/>3) Making it light and cheap enough to make using it worthwhile. Hi,
Great series. One idea to help with the reentry TPS challenge that I’ve been kicking around is a sacrifical “reentry drag chute”.

This would be some sort of parachute that you would deploy at the beginning of reentry and whose function is to provide extra drag as high as possible during rentry before buring up, thereby allowing a lighter & simpler main TPS.

In form it might look more like a solar sail than a conventional parachute. See

http://www.spacedaily.com/reports/NASA_To_Attempt_Historic_Solar_Sail_Deployment_999.html
In that article they mention one of its uses would be to de-orbit LEO satelites.

Alternatively maybe a fine mesh of stands of an ablative material might work better.

If it works as advertised it could make for an easier TPS problem, reduce g loads on re-entry and help maintain the proper orientation on reentry. It might be able to help with some about cases as well.

Its also something that could be tested with sub-orbital vehicles :-)

Key challenges would be to:

1) Getting enough usable drag before it burnt up.

2) Getting it deployed and keep it deployed in near vaccuum conditions as it would need a lot of surface area to be usefull.

3) Making it light and cheap enough to make using it worthwhile.

]]> By: Jon Goff http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2956 Jon Goff Mon, 23 Jun 2008 14:36:00 +0000 http://selenianboondocks.com/?p=511#comment-2956 Spacecadet,<br/>While you could add drop tanks, I think the best way to use them would be to use them the way military fighters do--as a way of enhancing capability. I don't think there's any military fighter craft that has to have drop tanks to perform its bare minimum mission. So, you make an orbital vehicle that can put a small payload up without drop tanks, but you use drop tanks for the occasional much bigger payload, or for giving you new capabilities you couldn't have had with drop tanks. Even if they're relatively cheap (lightweight tanks aren't really that cheap, especially in orbital LV sizes), you don't want to be tossing them every time if you can avoid it. But every once in a while? Sure. Of course that might require you to oversize your first stage, but that's not necessarily the end of the world--nothing says you need to always load a full load of propellant if it isn't needed.<br/><br/>~Jon Spacecadet,
While you could add drop tanks, I think the best way to use them would be to use them the way military fighters do–as a way of enhancing capability. I don’t think there’s any military fighter craft that has to have drop tanks to perform its bare minimum mission. So, you make an orbital vehicle that can put a small payload up without drop tanks, but you use drop tanks for the occasional much bigger payload, or for giving you new capabilities you couldn’t have had with drop tanks. Even if they’re relatively cheap (lightweight tanks aren’t really that cheap, especially in orbital LV sizes), you don’t want to be tossing them every time if you can avoid it. But every once in a while? Sure. Of course that might require you to oversize your first stage, but that’s not necessarily the end of the world–nothing says you need to always load a full load of propellant if it isn’t needed.

~Jon

]]> By: SpaceCadet http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2955 SpaceCadet Mon, 23 Jun 2008 04:28:00 +0000 http://selenianboondocks.com/?p=511#comment-2955 Nice article (and series)! TSTO popup has been my preferred option for a while. <br/><br/>Have you considered expendable drop tanks on the second stage? It's a mature technology for military aircraft. I wouldn't use them for LH2, too much like the Shuttle with ice & foam issues. <br/><br/>But for HC, maybe 30 to 40% of the fuel tankage could be outside the RLV, making it smaller & lighter. That plus losing part of the tank mass halfway to orbit, should give a fairly substantial gain.<br/><br/>Drop tanks should be quite cheap, compared to any other part of the dry mass. Nice article (and series)! TSTO popup has been my preferred option for a while.

Have you considered expendable drop tanks on the second stage? It’s a mature technology for military aircraft. I wouldn’t use them for LH2, too much like the Shuttle with ice & foam issues.

But for HC, maybe 30 to 40% of the fuel tankage could be outside the RLV, making it smaller & lighter. That plus losing part of the tank mass halfway to orbit, should give a fairly substantial gain.

Drop tanks should be quite cheap, compared to any other part of the dry mass.

]]> By: john hare http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2954 john hare Fri, 20 Jun 2008 20:02:00 +0000 http://selenianboondocks.com/?p=511#comment-2954 Jon,<br/><br/>I think my main assumption problem was that your pop up stage would fire from zero-zero horizontal and vertical velocity at 100 km altitude. From that assumption I can't get under 400-500 m/s gravity losses even with T/W of 1.4. <br/><br/>Firing from 80+ km with 500+ m/s vertical, it is easy to get under 200 M/S gravity losses with the 1.4 T/W. To eliminate the gravity losses entirely seems more difficult that staging at 50 km with 1,000 m/s vertical velocity and <100 m/s gravity losses.<br/><br/>Your observation that hydrogen stages nearly match kerosine stages make it a bit silly for me to attempt to figure an ideal velocity split. I don't have enough knowledge to spin this portion into a cost arguement. Jon,

I think my main assumption problem was that your pop up stage would fire from zero-zero horizontal and vertical velocity at 100 km altitude. From that assumption I can’t get under 400-500 m/s gravity losses even with T/W of 1.4.

Firing from 80+ km with 500+ m/s vertical, it is easy to get under 200 M/S gravity losses with the 1.4 T/W. To eliminate the gravity losses entirely seems more difficult that staging at 50 km with 1,000 m/s vertical velocity and <100 m/s gravity losses.

Your observation that hydrogen stages nearly match kerosine stages make it a bit silly for me to attempt to figure an ideal velocity split. I don’t have enough knowledge to spin this portion into a cost arguement.

]]> By: Jon Goff http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2940 Jon Goff Wed, 18 Jun 2008 02:54:00 +0000 http://selenianboondocks.com/?p=511#comment-2940 Paradox,<br/>Good catch! Glad you're enjoying the series.<br/><br/>~Jon Paradox,
Good catch! Glad you’re enjoying the series.

~Jon

]]> By: paradoxolbers http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2939 paradoxolbers Wed, 18 Jun 2008 01:16:00 +0000 http://selenianboondocks.com/?p=511#comment-2939 Wonderful set of posts on OrbAccMethods! A trivial text change for u. In your first set of bulleted points, under Benefits, number 8 should read:<br/><br/>Since the first stage has *no* downrange velocity, its<br/><br/>best,<br/>Paradox Olbers in Second Life Wonderful set of posts on OrbAccMethods! A trivial text change for u. In your first set of bulleted points, under Benefits, number 8 should read:

Since the first stage has *no* downrange velocity, its

best,
Paradox Olbers in Second Life

]]> By: john hare http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2932 john hare Tue, 17 Jun 2008 01:35:00 +0000 http://selenianboondocks.com/?p=511#comment-2932 Jon Goff said... <br/>redneck,<br/>Any "vertical angle" you give the stage starts reintroducing gravity losses. Ie some component of the velocity is now counteracting gravity, and not going to accelerating the stage. So you're not actually gaining anything. I'm not entirely sure how much time you gain by raising the first stage apogee (thus allowing a lower upper stage T/W and longer acceleration to orbital velocity). I'll have to see if I can figure out an approximation of the relationship.<br/><br/>===========================<br/>I will try to figure out a coherent relationship in a few days for the velocity split. I believe the gravity losses are less if you begin thrusting earlier with a bit less vertical angle. I will try to organize that also when I feel like it. Just read about Len.<br/><br/>=================================<br/><br/>As for the hydrogen vs kerosene argument, it's worth noting that AFAIK, the best LOX/LH2 propellant mass fraction is only a tiny hair worse than the best LOX/Kero pmf. Ie, it at least appears historically that the density differences between the two propellants might not help as much as seems to be commonly argued in our circles. It could be that they just aren't trying as hard with the LOX/Kero stages, but the more likely answer is that there are other effects that are being glossed over...not sure.<br/><br/>==================================<br/>You are one of the people that can get me to reexamine my assumptions with a single sentence. <br/>=============================<br/><br/>~Jon Jon Goff said…
redneck,
Any “vertical angle” you give the stage starts reintroducing gravity losses. Ie some component of the velocity is now counteracting gravity, and not going to accelerating the stage. So you’re not actually gaining anything. I’m not entirely sure how much time you gain by raising the first stage apogee (thus allowing a lower upper stage T/W and longer acceleration to orbital velocity). I’ll have to see if I can figure out an approximation of the relationship.

===========================
I will try to figure out a coherent relationship in a few days for the velocity split. I believe the gravity losses are less if you begin thrusting earlier with a bit less vertical angle. I will try to organize that also when I feel like it. Just read about Len.

=================================

As for the hydrogen vs kerosene argument, it’s worth noting that AFAIK, the best LOX/LH2 propellant mass fraction is only a tiny hair worse than the best LOX/Kero pmf. Ie, it at least appears historically that the density differences between the two propellants might not help as much as seems to be commonly argued in our circles. It could be that they just aren’t trying as hard with the LOX/Kero stages, but the more likely answer is that there are other effects that are being glossed over…not sure.

==================================
You are one of the people that can get me to reexamine my assumptions with a single sentence.
=============================

~Jon

]]> By: Jon Goff http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/comment-page-1/#comment-2928 Jon Goff Mon, 16 Jun 2008 12:34:00 +0000 http://selenianboondocks.com/?p=511#comment-2928 Mike,<br/>I talked about that a little in part 2 of the series. But basically, especially if you're in a high-flight rate operations mode, down-range recovery implies additional ground crews, additional areas setup as launch sites, additional launch licenses, additional insurance as Michael points out, etc. There are ways for the first stage to impart downrange velocity while still landing back at the launch site. But that's the topic of the next two or three (or maybe four) parts of the series.<br/><br/>~Jon Mike,
I talked about that a little in part 2 of the series. But basically, especially if you’re in a high-flight rate operations mode, down-range recovery implies additional ground crews, additional areas setup as launch sites, additional launch licenses, additional insurance as Michael points out, etc. There are ways for the first stage to impart downrange velocity while still landing back at the launch site. But that’s the topic of the next two or three (or maybe four) parts of the series.

~Jon

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