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Old 12-26-2011, 11:56 AM   #46
garyw
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Originally Posted by Napalm42 View Post
 Sounds perfectly reasonable, even with only 90 km/s, 3.5 would basically guarantee you'd have fuel to do some sort of ghastly muck up and still have plenty to come home with.
Remember that not only will the mothership need to get to mars and back home but it will also serve as an orbital fuel fort for the XR-2's that explore Mars. It's one reason why additional fuel is being shipped to Mars.
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Old 12-27-2011, 04:43 PM   #47
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Eh, forgot about that... Still, some wiggle room should still be present.
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Old 12-31-2011, 12:53 AM   #48
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Can someone get me the dV available to those Mars comm sats we're launching?
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Old 12-31-2011, 05:04 PM   #49
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Roger.

According to River Crab's table on the DSCS, dV = 2.017 km/s
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Old 12-31-2011, 05:08 PM   #50
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I have looked over this a bit. What kind of launch proposal are we doing? A direct-launch with solid fuel, or a 30-day circular ionic approach, which will be approximately 2.5-10% of our weight in fuel, compared to about 50-60% of our fuel if we are doing a full-on blast for 18 minutes to get that way.

I believe that doing an ionic approach, may be better in the long-term approach, so we can carry more mass.
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Old 12-31-2011, 06:27 PM   #51
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Originally Posted by Lord Wasteland View Post
 I have looked over this a bit. What kind of launch proposal are we doing? A direct-launch with solid fuel, or a 30-day circular ionic approach, which will be approximately 2.5-10% of our weight in fuel, compared to about 50-60% of our fuel if we are doing a full-on blast for 18 minutes to get that way.

I believe that doing an ionic approach, may be better in the long-term approach, so we can carry more mass.
For which mission? What 30 day approach? It takes around 7 months to go to Mars. Maybe I am missing something here but what are you talking about?
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Old 12-31-2011, 06:54 PM   #52
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 Roger.

According to River Crab's table on the DSCS, dV = 2.017 km/s
Hmm, slowing down may be a problem then. Most of the trajectories I've found have arrival dV in the 3.x km/s area. The folks flying those missions may have to try some light aerobraking, a la MRO. If they can handle that, they'll have enough fuel to get into orbit fine.

Gary, Lord Wasteland is talking about electric propulsion. And unless he has the software or the math handy to show how he intends to get to Mars in 30 days on modern electric propulsion, we aren't considering it.

Btw, sorry I don't have that tech memo written concerning the Mars trajectories. THis time of year is always fairly busy. That said, I'm confident now that everything big has been taken care of and we can get going on OFMM-P1.
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Old 12-31-2011, 06:56 PM   #53
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 Gary, Lord Wasteland is talking about electric propulsion. And unless he has the software or the math handy to show how he intends to get to Mars in 30 days on modern electric propulsion, we aren't considering it.
Ahh! Thanks for explaining that and we aren't using it. We are sticking with good old fashioned chemical rockets - besides which part of the mission counts on it take a few months to get to Mars whilst other planning goes on so it wouldn't be good if the missions were too quick!
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Old 12-31-2011, 07:42 PM   #54
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Originally Posted by Arrowstar View Post
 Hmm, slowing down may be a problem then. Most of the trajectories I've found have arrival dV in the 3.x km/s area. The folks flying those missions may have to try some light aerobraking, a la MRO. If they can handle that, they'll have enough fuel to get into orbit fine.
I don't think the DSCS has a heat shield though. Does the Jarvis have some sort of a upper stage? Or should we attach one of those paracone things, if it is possible?

Last edited by Pipcard; 12-31-2011 at 07:47 PM.
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Old 12-31-2011, 07:48 PM   #55
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 I don't think the DSCS has a heat shield though. Does the Jarvis have some sort of a upper stage?
They don't need heat shields. Read up on the MRO Mars orbit insertion and capture; MRO didn't have TPS either. What you do is use your engine to slow down into a closed orbit, and then dip the periapse into the atmosphere slightly and pick up the correct apoapsis over the course of a few weeks or months. After you're done, raise the orbit out of the atmosphere and you're all set. No heat shield needed.
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Old 12-31-2011, 08:10 PM   #56
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 I don't think the DSCS has a heat shield though.
Not required.

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 Does the Jarvis have some sort of a upper stage?
Yes. it has several types of upper stage. However, there are other stages out there so we can use any we want (And it can carry) - why?
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Old 12-31-2011, 08:24 PM   #57
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Originally Posted by Arrowstar View Post
 They don't need heat shields. Read up on the MRO Mars orbit insertion and capture; MRO didn't have TPS either. What you do is use your engine to slow down into a closed orbit, and then dip the periapse into the atmosphere slightly and pick up the correct apoapsis over the course of a few weeks or months. After you're done, raise the orbit out of the atmosphere and you're all set. No heat shield needed.
Oh, okay! I forgot about the "multiple orbits over a few months" type of aerobraking. I only thought about the "fast and hot" aerobraking.
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Old 12-31-2011, 08:50 PM   #58
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 Oh, okay! I forgot about the "multiple orbits over a few months" type of aerobraking. I only thought about the "fast and hot" aerobraking.
Why? Where did anyone say that?

Carrying a heat shield = weight and pointless for orbiting probes especially as we:

1. Want them in a high orbit.

2. Will carry three per rocket. i.e. additional weight for heat sheilds.
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Old 12-31-2011, 09:00 PM   #59
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Yeah, we'll be okay if we don't have to lower apoapse too much. Put the comm sats into a nice, highly elliptical orbit with their engines, lower apoapse the (hopefully small) required amount, and raise periapse out of atmosphere. Easy.
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Old 12-31-2011, 09:05 PM   #60
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 Why? Where did anyone say that?
Because I forgot about the slow and safe method.
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