OFMM General Discussions Archive

[eyu100]

Doesn't Orbiter measure specific impulse in units of speed? Other than that, I can't see anything wrong with the graph from the graphing calculator; remember that delta-v is in m/s and mass is in kg, so the big numbers on the graph aren't actually that big.

 

[Bj]

Doesn't Orbiter measure specific impulse in units of speed? Other than that, I can't see anything wrong with the graph from the graphing calculator; remember that delta-v is in m/s and mass is in kg, so the big numbers on the graph aren't actually that big.

Oh yes right forgot about the km part.
And that means I divide 16500/9.18 to convert to Isp measured in seconds right?

In that case we have an Isp of 1797.38

which gives us approximately 98,900kg giving its all. -Probably more realistic I think.. asuming the dv is accurate as well.

Otherwise from the way I have it before, this engine will push
1,475,290kg to Mars giving its all. :hmm:

 

[Wolfer]

That it will take approximately 6.12 km/s DV from LEO to LMO.

We can reduce that by aerobraking into Mars orbit.

Also for your graphs, the second one looks okay.
Using the data you gave I have
dv= 16500*ln((100466+x)/(42000+x))
which gives, in m/s and kg:

 

[Bj]

We can reduce that by aerobraking into Mars orbit.

For parts that have heat shields and whatnot, but you realize this would be for the MSS... like putting a huge heat shield over the ISS. I am pretty sure the joints, solar panels and connecting pieces where not meant to take a lot of wind resistance & heating. :thumbup: also lugging around a heatshield of that size would cause more weight then its worth.

This would only work for vessels capable of aerobraking, though if there are vessels that are capable, then that would help quite a bit.

 

[Salun]

Well while I was at work I had a sort of brain storm involving the LOSPS. Rather than using say the Carina 2 satellites perhaps it would be more prudent to use the UCGO unfolding satellite. As the weight less and with a dedicated launcher or heavily modded one. Rather than one rocket. One launch one satellite. Hows about one Rocker one launch. 6 satellites. Which would provide an uninterrupted signal to base and back. Provide weather recon on the martian surface and act as a global martian Positioning system.

http://www.orbiter-forum.com/showthread.php?t=14057
Case in point

 

[Izack]

For parts that have heat shields and whatnot, but you realize this would be for the MSS... like putting a huge heat shield over the ISS. I am pretty sure the joints, solar panels and connecting pieces where not meant to take a lot of wind resistance & heating. :thumbup: also lugging around a heatshield of that size would cause more weight then its worth.

This would only work for vessels capable of aerobraking, though if there are vessels that are capable, then that would help quite a bit.

Could this be where multiple smaller transfer vehicles become useful? :hmm:

 

[Salun]

Could this be where multiple smaller transfer vehicles become useful? :hmm:

All honesty IM starting to think im the guy designing the coms system but I can say is IM against shielding the whole ship so it can take a dip into the martian atmosphere for ten minutes. Though I do recall a few years back messing around with the concept of using the Tether MFD to aerobrake. Using say a Shuttle A cargo pack and attaching it tot he shuttle with the Tether MFD. Very far fetched but I think a million times better than adding tons of weight to mars and back costing more fuel and power.

 

[Pablo49]

I was thinking about the UCGO satellites earlier. Never saw that adapter before. Great idea, Salun.

I'm also against the aerobraking idea. I'd rather just use the stack's own engines and burn retrograde to get into orbit. If we are making our own fuel on the planet's surface, wasting fuel for orbit insertion isn't a big deal.

 

[Arrowstar]

Well, it's really not a fuel wasting issue, though I suppose that can be part of it. The more fuel you require to stop at Mars, the less payload you can bring because your payload mass has partially been replaced with fuel mass. Aerobraking has the benefit of allowing more payload mass, so long as the heat shield isn't larger than the fuel required to stop, as well.

 

[Bj]

Could this be where multiple smaller transfer vehicles become useful? :hmm:

How so?

I was thinking about the UCGO satellites earlier.

I'm thinking those satellites that came with DGIV (I think) would work good too. Ill add it to the list

Well, it's really not a fuel wasting issue, though I suppose that can be part of it. The more fuel you require to stop at Mars, the less payload you can bring because your payload mass has partially been replaced with fuel mass. Aerobraking has the benefit of allowing more payload mass, so long as the heat shield isn't larger than the fuel required to stop, as well.

Yes think of it this way, if we have 98,900kg absolute maximum, with only a single tank load, that is much less than a single payload from the Ares V. So what is that, like 4 modules space shuttle sized?

Note: after a quick check, if we load a AresV full of fuel (160,000kg) onto the MSS, we can jump our payload up to 484,474kg.

Which makes me think, how long of a burn would it take for so much fuel?

Reversing Specific impulse equation:

[math]1500000/9.18 = 1797.38 * \frac{42000+160000}{\bigtriangleup t} [/math]

[math] ~90.91 = \frac{202000}{\bigtriangleup t} [/math]

which turns to ~2221.98 seconds or 37.03 minutes. Ouch:blackeye:... but still doable.

Well anyway more planning tomorrow.

 

[Salun]

How so?



I'm thinking those satellites that came with DGIV (I think) would work good too. Ill add it to the list




Yes think of it this way, if we have 98,900kg absolute maximum, with only a single tank load, that is much less than a single payload from the Ares V. So what is that, like 4 modules space shuttle sized?

Note: after a quick check, if we load a AresV full of fuel (160,000kg) onto the MSS, we can jump our payload up to 484,474kg.

Which makes me think, how long of a burn would it take for so much fuel?

Reversing Specific impulse equation:

[math]1500000/9.18 = 1797.38 * \frac{42000+160000}{\bigtriangleup t} [/math]

[math] ~90.91 = \frac{202000}{\bigtriangleup t} [/math]

which turns to ~2221.98 seconds or 37.03 minutes. Ouch:blackeye:... but still doable.

Well anyway more planning tomorrow.

Maybe with the launch from earth(Or moon) We can add a little power with SRB's that disengage like the shuttles after fuel consumption. Great way to add a lot of power with minimal weight gain.

 

[Richy]

I like to see a trans-martian stack ejection with boosters out of earth SOI. But that's just an opinion of a spectator.

 

[Columbia42]

The Ares V already has boosters. However we could add two more to increase its payload.

 

[Izack]

More power!!

:lol:

Anyway...
If the payload were divided among smaller craft (say, two shuttle-sized modules end to end and a pile of cargo), the mass of the heat shields (inflatable, I assume) could be greatly reduced. Of course, then we have to fuel 3-4 engines instead of one...It really depends on how fast or how efficient you want it to go.

I'm just shooting ideas now, but is it possible to send less up with the crew, and Hohmann an unmanned cargo vessel over so it arrives a couple months into the mission?

 

[dnt462]

Don't think I've seen that word used as verb before(hohmann). But maybe I've just missed other times.

 

[Izack]

Don't think I've seen that word used as verb before(hohmann). But maybe I've just missed other times.

It isn't supposed to be used as a verb. It's a surname and an adjective for a type of low-energy transfer. I was speaking colloquially.

As a side note, I believe this is the first time I've been on the receiving end of a grammar lecture.

 

[PhantomCruiser]

Isn't "google" now accepted as a verb? Actually the use of Hohmann in that context made perfect sense to me...

 

[Bj]

Isn't "google" now accepted as a verb? Actually the use of Hohmann in that context made perfect sense to me...

You know your an Orbiter fan when... :thumbup:

I like to see a trans-martian stack ejection with boosters out of earth SOI. But that's just an opinion of a spectator.

going from the current mss concept, (btw good job Pablo) it would be rather difficult to start sticking SRB's onto this and boosting it, for few specific reasons;

1. How do you get a fueled SRB into orbit?
2. SRB has a way low Isp, 269 -means it burns through a ton of fuel much faster than a higher Isp engine would, which in this case Nerva has is ~1800. So the Nerva will get more dV per kg of propellant. More logical, I think to strap 2x Nerva together and cut burn time by half or payload by 2.

:lol:

Anyway...
If the payload were divided among smaller craft (say, two shuttle-sized modules end to end and a pile of cargo), the mass of the heat shields (inflatable, I assume) could be greatly reduced. Of course, then we have to fuel 3-4 engines instead of one...It really depends on how fast or how efficient you want it to go.

I'm just shooting ideas now, but is it possible to send less up with the crew, and Hohmann an unmanned cargo vessel over so it arrives a couple months into the mission?

Ok but, if you look at the parts going with the MSS...

• A: Habitation modules (3) (12 astronaut capacity)
• B: Cupola and Command Center
• C: Service module
• D: Communications truss
• E: Generic work modules (2)
• F: Generic storage modules (3)
• G: Solar arrays (2)

Everything is really important, don't you think? Well if not you can be the guy to tell the crew they don't get any solar panels or hab modules, or food or...


Anyway, lets just pretend we get a heat shield that would cover the MSS entirely.

That would lower our required DV to 4.72km/s. (assuming aerocapture not aerobraking)

That would put us up to 148,479kg (using main fuel only, no drop tanks) from a payload of 98,900kg. Which puts us up at a 49,579 increase in payload(assuming no weight added for shield).

If the heat shield would weigh less than 49,579 then it might be worth it.

Now going off this;

http://en.wikipedia.org/wiki/File:800px-ShuttleTPS2col.png

FRSI has 1.60 kg/sq m - below 700 F
LRSI has 3.98 kg/sq m - below 1,200 F
HRSI has 9.20 kg/sq m - below 2,300 F
RCC has 44.66 kg/sq m - exceed 2,300 F

I can't go much farther because I don't really know how to calculate the skin temperature of a vessel or even estimate it.

Anyway, aerobraking has a big bonus. As long as it might be structurally sound it might be worth it.

 

[Bloodworth]

:lol:

Anyway...
If the payload were divided among smaller craft (say, two shuttle-sized modules end to end and a pile of cargo), the mass of the heat shields (inflatable, I assume) could be greatly reduced. Of course, then we have to fuel 3-4 engines instead of one...It really depends on how fast or how efficient you want it to go.

I'm just shooting ideas now, but is it possible to send less up with the crew, and Hohmann an unmanned cargo vessel over so it arrives a couple months into the mission?

I think aerobreaking the stack would be a mistake. A stack simply is not intended to take that kind of stress. Heatshields or not, the sheer stress of plunging that thing into the atmosphere would rip it apart. It is afterall held together mostly with airlocks and other assorted docking ports. The sheer size of the heatshield needed (even if it is inflatable) is space and weight that could be better used elsewhere or left behind altogether.

Lol, the verb made perfect sence to me
Why yes, we could hohmann over some cargo, but if it arrives months into the mission, we will be at mars without possiblly necessary supplies. Not to mention the fact that with my luck, the thing would either miss mars altogether or smack into the planet. Lol, with MY luck the aiming would be a little TOO good and the thing would impact dead center of the base:rofl:

 

[Wolfer]

We could always place the modules in a way to minimize stress on the attachment points and make said attachments a bit sturdier (simulate this by giving them some more mass to the modules?). The modules alone can handle the acceleration as long as it's not too high, they've been launched on rockets after all.
We can also reduce the deceleration needed to do an aerocapture if we do it in multiple steps. ie: Aerobrake into a high elliptical orbit-> then into a less eccentric orbit-> continue process until desired ApA is attained-> circularize.