ESAS draft report is out!

[dobbins]

"I guess I care more about routine access to space."<br /><br />Routiine aceess to space is decades away.<br /><br />"I want to see us make access to/from LEO safer, more affordable, and more routine"<br /><br />Cheap access to space is decades away.<br /><br />"spending NASA's entire budget to send 4 people to the moon two or three times per year."<br /><br />Any new space plane will eat NASA's manned budget for a handful of go nowhere LEO flights each year.<br /><br /><br /><br />

 

[centsworth_II]

<font color="yellow">"Also, a lot of you differentiate between "going in circles" in LEO and "actually going someplace" by returning to the moon. Well, to me, it's going in circles either way. <b>You're still orbiting the Earth on the moon, after all!"</b></font><br /><br />Still not a single mention of the new SCIENCE that will be done on the Moon. Its like comparing a trip to Walmart and a trip to the Modern Museum of Art by saying <b>"what's the big deal, you're still just driving to a big building and back home again."</b> <div class="Discussion_UserSignature"> </div>

 

[henryhallam]

<font color="yellow"><br />200 m/s seems like an insignificant price to pay for double the ISP of chemical rockets. </font><br />Absolutely! I was just trying to think of a reason to use such a high orbit assuming NTR was not to be used.<br /><br />Thanks for the link to the RORSAT page. I had no idea so many reactor-powered satellites were launched! Had thought it was just one or two.

 

[vt_hokie]

<i>Still not a single mention of the new SCIENCE that will be done on the Moon.</i><br /><br />What great science will be done during these weeklong excursions to the lunar surface that will justify the cost, and wil justify gutting NASA's other science programs as is happening right now?

 

[vt_hokie]

<i>Any new space plane will eat NASA's manned budget for a handful of go nowhere LEO flights each year.</i><br /><br />There's no reason that it has to. We have the technological capability to design and build a space plane that will be much safer and cheaper to operate than the space shuttle, certainly.

 

[themanwithoutapast]

"What great science will be done during these weeklong excursions to the lunar surface that will justify the cost, and wil justify gutting NASA's other science programs as is happening right now? "<br /><br />It is not wise to start with long-term (6months) excursions to the moon right away, hardware and procedures have to be tested first in short-term (4-7days) excursions. How many of the short-term excursions there have to be before staying longer will have to be determined, as I see it, there will only be 3-4 before switching to a long-term (permanent) moon base of 4 crew members with rotating crews every six months. (when I say "moon base" I solely mean 2-3 of the 20ton lunar cargo moduls linked together).

 

[mlorrey]

That is absurd. ISS is the test bed for long term excursions. The only short term excursions to the lunar surface should be construction gigs to bring hab modules and assemble them together. Once those are done, long term crews and the logistics to support them should be kept in constant rotation.

 

[themanwithoutapast]

I am not disagreeing with you, still a minimum of 3-4 weeklong missions (say in the time-frame 2018-2020) are still needed before any long-duration crew can go.

 

[vt_hokie]

Well, regardless of what happens with ESAS, I will never stop holding out hope for something like this:<br /><br />http://img383.imageshack.us/img383/8793/147xj.jpg<br /><br />This generation and the next should have more to look forward to than a few Apollo style lunar excursions using antiquated hardware at a cost of billions to U.S. taxpayers. When I was a child, we were told that many of us might actually get to fly in space! Now, we're resigning ourselves to 1960's style spaceflight, even down to the primitive capsule design, and only a handful of elite NASA astronauts will get to fly aboard the "CEV" two or three times per year. That is not the way to open up the space frontier.

 

[josh_simonson]

Oh cool, instead of having the orbiter next to the ET, you put it UNDER the ET, with no escape system. Are you per chance in the funeral buisness?

 

[gunsandrockets]

"Oh cool, instead of having the orbiter next to the ET, you put it UNDER the ET, with no escape system. Are you per chance in the funeral buisness? "<br /><br />Acch! Let's not get into a debate about the merits (or lack) of spaceplanes or the Starclipper on this thread, okay? This thread is about the formal ESAS plans and there is lots to examine and plenty to interest anyone.<br /><br />That said here I go violating my same plea, for in defense of the Starclipper it doesn't use brittle ceramic TPS like the Space Shuttle, nor would it neccessarily lack a crew escape system either. There are more launch escape systems than Apollo style tractor tower rockets; there are ejection seats like in the Gemini and X-15 and other possibilites such as an escape pod system similar to that in the F-111 or an escape capsule system similar to that in the B-70.

 

[vt_hokie]

<i>National Space Programs should be far more ambitious.</i><br /><br />That's just it. I view the "CEV" as being far less ambitious than it should be. They went with the simplest, cheapest, easiest to implement option. Hell, NASA didn't even give the competing contractors a chance to show any innovation in the CEV design, and shot down Lockheed's lifting body proposal by mandating the Apollo Command Module rehash design. Our national space program should be able to do better. And I would point out that going with the cheapest to develop option will result in spending more on operations in the long run. If we focus on reducing launch costs now, as was the goal with VentureStar, we will save so much more in the long run, while opening up the space frontier to a far greater number of people and payloads.<br /><br />I do like the idea of the "Shuttle Derived Heavy Lift Vehicle", except for the plan to throw away expensive SSME's on every flight. That's one part of the plan I can't disagree with. But the CEV/SRB stick combo for our nation's next generation crew transport is just pathetic, imo. <br /><br />As for private concerns like Scaled and Virgin Galactic, I don't hold out much hope for a groundbreaking, safe, robust orbital system any time in the near future. I'm a huge fan of Burt Rutan and I hope that his Mach 3 suborbital SS2 is a huge success, but that's a hell of a long way from an orbital vehicle, much less an orbital vehicle with the type of redundancy, robustness, and safety that NASA would demand. SpaceShipTwo is to Lockheed's StarClipper what a Cessna 182 is to a Boeing 747! It'll be a long time before private industry can produce a space shuttle class vehicle, I'm afraid. It would take 100 Paul Allens to fund it, as the up-front development costs are tremendous, even if well worthwhile in the long run.

 

[gunsandrockets]

"Thanks for the link to the RORSAT page. I had no idea so many reactor-powered satellites were launched! Had thought it was just one or two. "<br /><br />I was surprised too. An interesting footnote to the secret history of the Cold War.<br /><br />Now back to the NASA DRM for Mars. The cargo missions look tailor made for a reusable nuclear-electric-propulsion tug. I know that once upon a time you were crunching the numbers for a lunar NEP tug. Could you apply your earlier work to a Mars tug? I would like to see the results of that.<br /><br /><br />I imagine a Mars NEP tug using a lot of flyby maneuvers to assist it's flight. I found a paper sometime ago that suggested a tug could use lunar flyby to assist return to Earth. I think the benefit was around 1.5 km/s. I also think that if the tug split off from it's cargo while approaching Mars (the cargo then using aerocapture), the tug could do a flyby of Mars on it's first pass, get a gravity assist and begin to return to Earth.

 

[JonClarke]

" but the slower cargo-prepositioning missions would be perfect for NEP. "<br /><br />Hmmm. How many new propulsion systems do you want to develop here? NEP plus NTR? <br /><br />"There's a significant difference (something like 200m/s at a rough guess) between a 500km and a 1000km circular orbit... 200 m/s seems like an insignificant price to pay for double the ISP of chemical rockets."<br /><br />Do have a reference for this? I have been trying to chase these numbers down. But the numbers are going to be a larger than 200 m/s. the NTR departure orbit is going to be as high as 1200 km, whereas a chemical stage will depart from as low as 200 km. I don't know the velocity difference here. If anyone has the actual difference this makes I would be most interested. <br /><br />Also remember that NTRs are much heavier. Current concepts for a NTRs have engines of 6.8 tonne thrust massing 2.2 tonnes. A LOX-H2 engine such as an SSME will deliver 232 tonnes of thrust on only 50% more mass. This eats into the advanatages of that 900 sec Isp, as does the need for reserve fuel to ensure the engine enters a safe disposal orbit. <br /><br />I agree that a resuable SSTO on Mars would be very useful. But it would be a very risky item to have on the first mission.<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[krrr]

<font color="yellow">But the numbers are going to be a larger than 200 m/s. the NTR departure orbit is going to be as high as 1200 km, whereas a chemical stage will depart from as low as 200 km. I don't know the velocity difference here. If anyone has the actual difference this makes I would be most interested.</font><br /><br />200 km: 7784 m/s<br />500 km: 7669 m/s<br />800 km: 7452 m/s<br />1200 km: 7253 m/s<br /><br />x km: sqrt(3.986005e11/(x+6378.1))

 

[gunsandrockets]

krrr, Shoudn't the delta V increase with altitude? Your numbers decrease instead!<br /><br />Even so, it's clear that the figure henryhallam first suggested is pretty close. The relevant altitudes to examine are 400 km and 800 km. And extrapolating from krrr's numbers, that difference appears to be around 200 m/s.<br /><br />And anyway, in a practical sense the difference between assembling an MTV at 800 km as opposed to 400 km is zero. That's right zero. Any extra delta V needed to assemble the MTV at higher altitude is equally subtracted from the delta V the MTV needs to accomplish it's mission. It's an exactly equal tradeoff.<br /><br />Or in other words, it doesn't take more launch vehicles to build a Mars ship in a higher than normal Earth-orbit, because the higher the orbit the smaller the Mars ship would need to be.<br /><br />

 

[gunsandrockets]

"[...]while the MTV loiters in a circular orbit of 800- to 1,200-km altitude."<br /><br />When they see 'MTV', are people going to think 'Music Television' instead of 'Mars Transit Vehicle'? Maybe NASA should choose a different acronym! <br />

 

[gunsandrockets]

"Hmmm. How many new propulsion systems do you want to develop here? NEP plus NTR?"<br /><br />NEP is a natural outgrowth of meeting the power supply requirements of long stays on the lunar surface. If a space power nuclear-reactor is developed for moon missions, it's a simple matter to use it as a power source for ion rockets too.

 

[gunsandrockets]

"Also remember that NTRs are much heavier. Current concepts for a NTRs have engines of 6.8 tonne thrust massing 2.2 tonnes... This eats into the advanatages of that 900 sec Isp,..."<br /><br />Current concepts of NTRs are also bi-modal. Which means the NTR not only propels the ship it also supplies the ship's electrical power thereby eliminating the mass of a more typical power system.<br /><br />And even though NTR does not have the thrust to weight ratio of a chemical rocket, it has enough T/W for typical maneuvers such as orbital capture. Otherwise the only important thing is the NTR's higher ISP. For the mass of propellent will dwarf the remaining mass of a spacecraft, whether it's chemical or NTR.

 

[spacester]

<font color="yellow">200 km: 7784 m/s <br />500 km: 7669 m/s <br />800 km: 7452 m/s <br />1200 km: 7253 m/s <br /><br />x km: sqrt(3.986005e11/(x+6378.1)) </font><br /><br />It appears those numbers are orbital velocities.<br /><br />I calculate dV between orbits using orbital energy.<br /><br />A 200 km circular orbit has 3.2208E7 J/kg specific energy<br />A 1200 km circular orbit has 3.6207E7 J/kg specific energy<br /><br />E/m = Orbital Energy = GM (1/Re - 1/(2*Rc) )<br />GM = 3.987e14 N - m^2 / kg<br />Re = 6378 m<br />Rc = Re + altitude of circular orbit<br />m = mass of spacecraft<br /><br />Using<br />E/m = 1/2 * v^2<br />aka<br />v = sqrt(2*E / m)<br />using<br />v = sqrt(2*(E/m)|2) for the final orbit, etc<br />then<br />dV = v2 - v1 = sqrt(2*(E/m)|2) - sqrt(2*(E/m)|1)<br /><br />I find that one needs<br />483.7 m/s to go from 200 km to 1200 km<br /><br />****<br />Why wont [SUB]1[/SUB] work? <b>bold </b> works . . ? <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

Ah! Now I get it.<br /><br />I see that the difference in delta V between altitudes is only slightly different from the difference in orbital velocities. Interesting.

 

[najab]

<font color="yellow">Why wont [SUB]1[/SUB] work?</font><br /><br />Because _subscripts aren't a part of UBBCode - you have to do them in HTML.

 

[henryhallam]

Here is an Excel spreadsheet to work out dV to move between any two circular orbits.

 

[JonClarke]

"And anyway, in a practical sense the difference between assembling an MTV at 800 km as opposed to 400 km is zero. That's right zero. Any extra delta V needed to assemble the MTV at higher altitude is equally subtracted from the delta V the MTV needs to accomplish it's mission. It's an exactly equal tradeoff."<br /><br /><br />No. Spcester can give you the fancy equations - forum coding permiting - <img src="/images/icons/smile.gif" /> but it is more efficient to "burn" propellant in low orbit as quickly as possible. Otherwise youy expend propellant to send it into a higher orbit. That is why the parking orbit of spacecraft on interplanetary missions are as low as possible, and propulsive captures always carried out on closest approach.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Thanks spacester, Roughly then you need 0.5 km/s more to reach a 1200 km orbit.<br /><br />If the SDLV can carry 125 tonnes to a 400 km orbit, what can it carry to a 200 km and a 1200 km orbit, respectively?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>