DG-TROTSKY to Mission Control KSC . . . Ready for Launch

[LTrotsky]

Mission Control (Orbitnauts) :

LTrotsky (pilot) DG-TROTSKY files, in accordance with the relevant procedures, the Final Pilot Flight Plan.

Mission NASA-STP 002 - Earth/Mars Transit and Return

Leave

2011.9264 12 4 2011

Arrive (Scheduled)

2012.6351 8 19 2012

Flight Plan :

1) D = 12-3-11 0800 local time : Launch using Launch MFD, target Mars

2) D+1 to 24 hours: Use this period to Align and configure TransX staging for transit

3) D+2 to 100 days: Cruise along flight plan

4) D+130 days : Mid Course Correction Burn (MCCB)

5) D+200 days : Final MCCB

6) D+258 days : Target Approach Adjustment Burn (AAB)

7) D+259 to D+260 days : Capture Phase. Enter Mars Orbit, Survey/Video/Photog (Screenshots)

8) D + 261 days : Mission Option. Determine feasibility of Insertion and orbit of 1 Martian moon.

9) D + 263 days : Return Orientation Phase. Begin vessel orientation for Earth Return.

10) D + 264 days : Earth Return Phase Commence. Mars Escape Burn.

11) D + 265 days to ? : Earth Return Cruise, Capture, De-Orbit, Re-entry.

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Considerations
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A - Sufficiency of Fuel for items 8 through 11, exclusive of 9, not determined. This is due in part to relative body orientation likely at the time.

B - Comments and Suggestions from Mission Control may be incorporated to FPFP at Pilot discretion.

(I will be getting a new computer, joystick, display, etc, in the next few days so feel free to make suggestions on that score also. Also donating to the site )

---------- Post added at 02:47 PM ---------- Previous post was at 02:37 AM ----------

Questions :

1) With a HTO (low energy transfer), it seems that on arrival Mars, the relative positions of Earth and Mars do not permit a time-efficient return. That is, Earth is deflected in it's orbit about 90 degrees prograde from Mars, and it is next to impossible to plot a return without some complicated maneuvers that essentially create a smaller ellipsis around the sun, transit of which permits the Earth to then "catch up" to the vessel, followed by an insertion burn to enlarge the vessel orbit and intercept Earth. Alternatively, one could just do a park orbit round mars and wait for an optimal eject window. Thoughts?

2) Is it possible to orbit the moons of Mars? They are very small.

3) What are some of the flight plans that people use for an efficient (time and fuel) Earth-Mars-Earth circuit?

 

[sorindafabico]

You can build a pseudo-orbit around the moons, but they aren't stable. There'a stock scenario about this , AFAIK.

For a non-stop round trip, you must wait for a launch window. But these launch windows aren't so frequent as one-way launch windows.

 

[boogabooga]

I hope that you don't expect to use launch MFD by itself to plan your launch.

 

[LTrotsky]

I hope that you don't expect to use launch MFD by itself to plan your launch.

Well, I have already tested it. It saves about 300kg fuel for me on the launch, but an align burn (actually several small align burns) are still necessary. What do you suggest?

 

[dgatsoulis]

This is from an old text note I had made for myself when I was learning about transfers and launch windows. You may find it useful.

[B][U]Finding a launch window to a planet. [/U][/B]
*(This is a simplification that assumes circular, coplanar orbits).
**(1 year = 365.25 days)

[B][U]Example1: Earth→Venus[/U][/B]
We will need the siderial period and the distance from the sun, so let's write those down. 
Earth: Dist = 1AU, Sid. Period = 365.25 days
Venus: Dist = 0.72 AU, Sid. Period = 224.7 days

Now let's find how long would a low energy Hohmann transfer to Venus take. 

We need the Semi Major axis of the transfer orbit:
We know the Aphelion is at Earth = 1AU and the Perihelion is at Venus= 0.72 AU.
So the SMa is (Pe + Ap)/2 = (0.72 + 1)/ 2 = 1.72/2 = 0.86 AU.

From the SMa we can calculate the period of the transfer orbit. 
Since we have the SMa in AU the period (in years) is simply:
[math] P^2 = a^3 \Rightarrow P = a^{1.5} = 0.86^{1.5} = 0.7975 \;\; years [/math] 
Remember that that's the whole period of the transfer orbit. The transfer itself is half the period: 
Transfer time = 0.7975/2 = 0.39875 years = 145.6 days.

During the transfer time, Venus will cover 145.6/224.7 = 64.8% of its orbit =233.3°
So Earth needs to be 233.3°-180° = 53.3° ahead of Venus at the time of the transfer.

Finally let's calculate the synodic period of Earth and Venus. This will tell us how often we can find an Earth→Venus launch window.

[math]Synodic \; period \; = \frac{1}{\left|{\frac{1}{SP1}-\frac{1}{SP2}}\right| }=\frac{1}{\left|{\frac{1}{365.25}-\frac{1}{224.7}}\right| }=\frac{1}{0.0017125274950219}=583.9 \;\;\; days \; = 1.6 \;\; years [/math]

[B][U]Example2: Earth→Mars[/U][/B]

Earth: Dist = 1AU, Sid. Period = 365.25 days
Mars: Dist = 1.52 AU, Sid. Period = 686.97 days

SMa of transfer orbit = (1+1.52)/2 = 1.26 AU
Transfer period = 1.26^1.5 = 1.414 years.
Transfer time = 1.414/2 = 0.707 years = 258.2 days
Mars will cover 258.2/686.97 = 37.6% of its orbit = 135.3° 
So Mars needs to be 180°-135.3° = 44.7° ahead from Earth at the time of the transfer.

[math]Synodic \; period \; = \frac{1}{\left|{\frac{1}{SP1}-\frac{1}{SP2}}\right| }=\frac{1}{\left|{\frac{1}{365.25}-\frac{1}{686.97}}\right| }=\frac{1}{0.0012821831451681}=779.9 \;\;\; days \; = 2.136 \;\; years [/math]

1) With a HTO (low energy transfer), it seems that on arrival Mars, the relative positions of Earth and Mars do not permit a time-efficient return. That is, Earth is deflected in it's orbit about 90 degrees prograde from Mars, and it is next to impossible to plot a return without some complicated maneuvers that essentially create a smaller ellipsis around the sun, transit of which permits the Earth to then "catch up" to the vessel, followed by an insertion burn to enlarge the vessel orbit and intercept Earth. Alternatively, one could just do a park orbit round mars and wait for an optimal eject window. Thoughts?

With the current plan you will have to wait approx. 1.5 Earth years for the window to Earth. Solution: Get there faster. A ~220 day transfer will allow you to arrive at Mars before the Mars →Earth window closes, with a wait time of less than a month.
At the launch from Earth, Mars will have to be 180°-((220/696.97)*360°) = 66.4° ahead from Earth on its path around the Sun.

2) Is it possible to orbit the moons of Mars? They are very small.

In theory yes. In order to be able to orbit a moon, its [ame="http://en.wikipedia.org/wiki/Roche_sphere"]Hill sphere[/ame] has to extend at least slightly out of the moon's radius. For Phobos I calculated a Hill sphere of 19.5 km from the center of the body.
In Orbiter, Phobos has a radius of 11 km, so the Hill sphere extends 8.5 km after that. Watch it though, with an escape velocity of ~11 m/s, you will need to orbit with 11/sqrt(2) ~ 7.7 m/s
Perturbations from Mars will probably kick you pretty fast, but you can always enter a pseudo orbit. Check out the \Navigation\Special orbits\Orbiting Phobos scenario for an example.

3) What are some of the flight plans that people use for an efficient (time and fuel) Earth-Mars-Earth circuit?

Make a search for "Mars" in the tutorials & challenges section of the forum. You will find several examples.
Keep in mind that there is no single "best" combination of fuel&time. It all depends on the capabilities of the spacecraft and the mission's parameters.

 

[LTrotsky]

Present Situation : As it turned out, the Mars trip here took from 4 December 11 to 2 August 12, which is 242 days, roughly 18 days ahead of the perfect HTO, and 22 days ahead of a viable timely return.

I have about 8.9k dv left in the tank. Fiddling with TranX, it seems I am just over the line of what I need to return. The return paths involve a sharp elliptical spiralling down towards the inner solar system, probably close to the Venusian elliptical, and comes back out to intersect the target. With the fuel I have, the closest I can get is around 4 million kilometers. I don't know if this even puts me in the Earth SOI with a trajectory that will allow capture at some point, assuming I have the fuel to de-orbit.

My current Mars orbit is .65 ecc, and the ellipsis is pointing at a bad angle. though I do have a 75km periapsis (my thought process was just burn enough for capture when I intersected the target, but it could have been much better I suppose). The return trajectories I have looked at involve a lot of outward dv, some prograde, and some plane change. The escape/eject burn shoots out from mars at about a 75 degree angle. This is all very bad in terms of fuel efficiency - as the most fuel efficient escape begins at periapsis, and for this to be an option that periapsis should be on the opposite side of the place you want to go (I think).

So the question now is, do I attempt to build a circular orbit so that I can with little fuel place the periapsis anywhere? Would this actually save some of the projected Dv needed to get back?

My experience so far with the Earth-Moon circuit is that you need about 3.5k Dv to have a reasonable chance of de-orbit. There are ways to do it that are very fuel efficient, like many orbits below 180 to 200km that will eventually slow you down (deteriorating orbits).

So I am a bit stymied at the moment.

What I am considering now is a burn that will put me on the outside of Earth's Orbit, within 10m km or so of the elliptical for a long time, then do a burn to essentially circularize that around the sun, and wait for Earth to catch up, where I should have enough fuel for some kind of approach and intersect. This is being considered because it can be accomplished with only about 1.5k dv, plus whatever is necessary to circ around the sun (maybe another 3k) But this seems more risky and possibly much less efficient than simply parking at Mars and waiting for a window.

Incidentally, as it turns out, Venus and Mercury are both deflected in the same area as earth, from 80 to 130 degrees "ahead" of Mars, so an inner solar system sling also doesn't seem possible.

What I have learned here is that mission planning involves more than using transX and nailing the target. Need a viable return plan too :facepalm:

---------- Post added at 01:38 PM ---------- Previous post was at 12:08 AM ----------

This screen captures the current situation of DG-LDT, and the 'dilemma'. The vessel is nearly at Mars periapsis. vector on the MFD display is counter-clockwise. The vector of the vessel on the Orbit MFD is clockwise, and the Earth's present distance and deflection is also indicated. Fuel remaining also visible, totaling 8.88k Dv main and 1.375k Dv RCS. The Surface MFD shows that the vessel is experiencing dynamic pressure from the Mars atmosphere at about 80km altitude.

[URL=http://s840.photobucket.com/user/LTrotsky/media/87178539-a9d3-47ee-a68c-139b6a9d0788_zps740dc1e1.jpg.html] [/URL]

Present periapsis cannot be used as an escape or eject point for return.

My sense of things is that the only real option for a return at this point is to establish a parking orbit at about 200km, and go into the hibernation module for the return window, in 2013.

 

[Enjo]

Well, I have already tested it. It saves about 300kg fuel for me on the launch, but an align burn (actually several small align burns) are still necessary. What do you suggest?

4th page of manual ("Target inclination"), subsection d), describes LaunchMFD's integration with TransX, which would put you into the correct parking orbit without alignment burns.

 

[LTrotsky]

4th page of manual ("Target inclination"), subsection d), describes LaunchMFD's integration with TransX, which would put you into the correct parking orbit without alignment burns.

Ah. Thanks. I really should read the add-on MFD documentation more thoroughly before I use it. :facepalm:

---------- Post added at 04:28 PM ---------- Previous post was at 02:08 PM ----------

With the current plan you will have to wait approx. 1.5 Earth years for the window to Earth. Solution: Get there faster. A ~220 day transfer will allow you to arrive at Mars before the Mars →Earth window closes, with a wait time of less than a month.
At the launch from Earth, Mars will have to be 180°-((220/696.97)*360°) = 66.4° ahead from Earth on its path around the Sun.

Again thanks for the info. The next Mars mission, STP-004, will attempt a 220 day transfer, and get inside the optimal return window (this will be simulated with UCCGO and missions to deploy fuel to the ISS, perhaps with a different ship). Prior to that, it will be necessary to equip the ISS for re-fuelling of the DG: as a safety measure, STP-004 will involve an LEO-Docking-Refuelling sequence prior to Mars transit. Meanwhile, STP-002 needs to get home

---------- Post added 10-19-13 at 01:44 AM ---------- Previous post was 10-18-13 at 04:28 PM ----------

Mission Control :

We are using the time in orbit around Mars to get some screen caps of various aspects of the Mars system. Our nearest pass to Phobos was 240km.

Experiencing difficulty with respect to inclination relative to Mars (edit : correction, see below). It keeps increasing about .06 degrees per orbit, with an Orbit time of about 15k/seconds. Given the amount of time before the Earth Return Window, this progressing is increasing the fuel needed for Earth alignment, endangering the mission.

Suspect, but do not know, Rinc progression due to eccentricity of orbit, which was established to get flybys of Phobos.

Solutions?

1. Circularize a high orbit - a parking orbit I guess is the term. Recommended altitude?

2. Ignore - correct with Eject burn at Mars Eject in 2013.

3. Ignore - correct with expending fuel for standard alignment burn(s).

4. Other?

Edit (Simdate : 2012/12-16 - DG-LDT inclination relative to MARS is holding at 10.00 degrees approx. The progression described above appears to be relative to the solar system ecliptic projection, which changes according to the inclination of Mars to that ecliptic. No corrective action taken as yet. Current burntime needed to align Earth is between 56 and 63 seconds. Earth return window, 11 months. I am beginning to wonder if Earth return is possible with approximately 8.5k/Dv left after alignment.

---------- Post added at 11:42 PM ---------- Previous post was at 01:44 AM ----------

STP-002x Mission Update

Mission Date : March 13,2013
Status : Orbiting Mars (eccentric, non-aligned)

Trans X is now reporting an Earth intersect with a maneuver that could begin September 15, 2013 which would take less than half of remaining fuel to perform and effect capture. This is now tentative date for Mars Escape and Earth Return Eject burn.

Fuel Remaining = 8975 Dv (Mains)
Maneuver Cost = 2,482.5 Dv
Capture Cost = 2,048 Dv
Encounter Nominal Target Altitude = 13,070 km (prograde)
Encounter Date = Sept. 6, 2014

---------- Post added 10-20-13 at 02:26 PM ---------- Previous post was 10-19-13 at 11:42 PM ----------

MJD : 56548.3180

Status : Orbiting Mars, ecc 0.3401, Rinc (Ecliptic 5.22, Earth 1.39 = Rinc 5.03)
Fuel : 8654 Dv main

Estimate approx 48 hours to Earth Return Window.

TransX reports the following:

Maneuver date : 56550.3172
Prograde : 994.6
ChangeP : 3.045K
Outward : 13.9
Encounter PeA : 592.8 km
Encounter MJD : 56869
Capture Dv : 804 Dv

Dv Remaining after Capture estimate : Approx 4k.

The TransX numbers will not hold for the next 48 hours, but should be within the above return interface parameters. Orbit will be aligned in next 48 hours and return trajectory re-calculated for this window.

---------- Post added at 03:06 PM ---------- Previous post was at 02:26 PM ----------

Mission Update

MJD : 56549.8736

Alignment accomplished.
TransX recalc reports target approach within nominal parameters. Close approach, low capture delta.
Final Alignment during next orbit (estimate less than 10 Dv).
Escape burn recalculation should remain nominal thereafter.

Mars Escape Burn begins 56550.3141.

---------- Post added at 03:55 PM ---------- Previous post was at 03:06 PM ----------

Visual Update :

[URL=http://s840.photobucket.com/user/LTrotsky/media/STP002x-HCSN042_mjd56550_transx_flight_fuel_data_zps7ee7e183.png.html] [/URL]

This doesn't look good, I know, but its the best I think I can do with the fuel remaining. Main problem is that the Eject burn has to take place nearly at Apoapsis, and I couldn't figure a way to change that without expending more fuel than I would save.

---------- Post added at 04:12 PM ---------- Previous post was at 03:55 PM ----------

Escape Burn completed.

5390 Dv fuel left in mains
275 Dv fuel left in RCS (not much)

Present target approach data is
MJD : 5872.2153
Alt : 3.849M (3,892km)
Capture Dv : 937.3 Dv

Will correct at 57550

---------- Post added at 09:43 PM ---------- Previous post was at 04:12 PM ----------

Earth now 37 million km away. Visualization image in the screenshots thread.

---------- Post added 10-21-13 at 03:34 AM ---------- Previous post was 10-20-13 at 09:43 PM ----------

Earth Orbit has been achieved. Relevant telemetry here.

[URL=http://s840.photobucket.com/user/LTrotsky/media/STP002x-HCSN048_mjd56872_De-Orbit_DecayingOrbit_data_zps69efd17f.png.html] [/URL]

Obviously, the low fuel situation is the biggest issue. I was lucky, not good, in that my orbit is prograde and will have a good re-entry profile for an approach to runway 33 at KSC.

However, the concern over fuel is so great that it seems I do not have enough to kill velocity for a standard re-entry. So, I did deliberately capture an eccentric orbit (to save fuel) and with a periapsis low enough that the atmosphere could be used over several passes to kill some velocity. The plan now is to use the orbits until lined up for a KSC re-entry to kill a little velocity at a time, so that during the re-entry I have more like the standard 7.45k Dv, rather than the 8.6 I have now. What do you all think?

I've already made one deterioration pass, with an AoA of 45. It was possible to hold attitude with very little RCS (holding down the control button while tapping the RCS thrusters), at the same time it was pretty clear that the DnP was bleeding off some of the v.