# Trajectory Office backroom

#### dgatsoulis

##### ele2png user
I don't think that there is a need to change the James Cook just because of the dv it can have when it's fully loaded with fuel, 2400 tons of it.

According to the mission roster, there are 6 missions that dock with the Cook for supplies:

One XR5 (OFMM 5), two DGIVs (OFMM 11 and 18), one ShuttleC (OFMM 12) and two XR2s (OFMM 21 and 22). Even if the payloads of the ships in these missions consisted entirely of fuel for the James Cook, it cannot have more than 467 tons of fuel, giving it a total dv of 127 km/s.

If the only refueling mission is the XR5 and you calculate a factor of 0.85 for the dead weight of the containers then you get 367.2 tons of fuel, giving a dv of 107,6 km/s, which is close to what the Arrow has.

#### garyw

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Good points dgatsoulis.

I was thinking of having the mars ship in orbit with 5-10% of fuel load anyway just for orbtial reboosts. That would be added to whatever is sent up in a couple of resupply missions - of course we also need to add other supplies for the crew so not every flight will be a fuel supply flight.

#### Arrowstar

##### Probenaut
Addon Developer
So we'll start with an empty Cook? That sounds like a plan. Don't screw up the fuel resupply missions!

---------- Post added at 11:37 PM ---------- Previous post was at 08:45 PM ----------

If the only refueling mission is the XR5 and you calculate a factor of 0.85 for the dead weight of the containers then you get 367.2 tons of fuel, giving a dv of 107,6 km/s, which is close to what the Arrow has.

That's still quite a bit. Even only loaded with that much fuel, there's almost no reason to optimize the Earth-Mars trajectory, as it can pretty much hit whatever target it wants, whenever it wants. If we want to make this more interesting, I might suggest limiting the fuel loads on the supply flights, maybe try to keep the available dV under 10 km/s or something.

Just a thought.

---------- Post added at 11:51 PM ---------- Previous post was at 11:37 PM ----------

Alright, looking at the departure numbers, if we want to do a Christmas departure in 2017 to send the Cook to Mars, here's my recommendation on parking orbit for the Cook:

SMA [km] | Ecc | Inc [deg] | RAAN [deg] | Arg. of Peri. [deg]
6678 (300 km agl) | 0 | 28.5 | 135 | 0

Keeping the Cook at a RAAN of about 135 degrees is important. I selected the inclination of 28.5 degrees because I believe that should be accessible from KSC, WIN, etc.

If we depart from this orbit, we're looking at about 3.5 km/sec of dV to place the Cook on a free return trajectory to Mars.

Comments?

#### Napalm42

##### Drell Admiral, Citadel Fleet
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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.

#### Arrowstar

##### Probenaut
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"Only" 90 km/s? :lol:

#### garyw

##### O-F Administrator
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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.

#### Napalm42

##### Drell Admiral, Citadel Fleet
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Eh, forgot about that... Still, some wiggle room should still be present.

#### Arrowstar

##### Probenaut
Addon Developer
Can someone get me the dV available to those Mars comm sats we're launching?

#### Napalm42

##### Drell Admiral, Citadel Fleet
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Roger.

According to River Crab's table on the DSCS, dV = 2.017 km/s

#### Lord Wasteland

##### Orbinaut
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.

#### garyw

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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.

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?

#### Arrowstar

##### Probenaut
Addon Developer
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.

#### garyw

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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!

#### Pipcard

##### mikusingularity
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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:

#### Arrowstar

##### Probenaut
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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. :thumbup:

#### garyw

##### O-F Administrator
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I don't think the DSCS has a heat shield though.

Not required.

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?

#### Pipcard

##### mikusingularity
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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. :thumbup:

Oh, okay! I forgot about the "multiple orbits over a few months" type of aerobraking. I only thought about the "fast and hot" aerobraking.

#### garyw

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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.

#### Arrowstar

##### Probenaut
Addon Developer
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.

#### Pipcard

##### mikusingularity
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Why? Where did anyone say that?

Because I forgot about the slow and safe method.

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