LRO / LCROSS

[astrosammy]

Now I even didn't get the TLI right. I think I'm to tired today, I'll restart tomorrow and then post what I did.

 

[Likeshadow]

I just discovered this forum discussing LCROSS. I can provide technical information if you are still interested, thruster coordinates, force levels, ISP curves, ACS modes, firing sequences, manuever planning, and just about anything about the spacecraft technically. I can also help with the 3d models if you want to add more detail and get scaling correct (unfortunately the actual models are proprietary so I can't just give them out). I also have access to all the pictures taken of the spacecraft in various developmental stages as well. We launch LCROSS June 17th, and I would be happy to help out anyone interested in this very exciting unique mission.

 

[BrianJ]

Hello and welcome Likeshadow
Thanks for taking the time to drop by and say hello, and also for the kind offer of information!

I can provide technical information if you are still interested, thruster coordinates, force levels, ISP curves, ACS modes, firing sequences, manuever planning, and just about anything about the spacecraft technically.

Yes please! All info you can provide will be gratefully received. Even if it's not immediately relevant to the simulation within Orbiter, there's plenty of folks here who will enjoy the extra insight into the mission.

Stuff I'd like to know (that I can think of right-now):

Launch window on the 17th June?

Preliminary selection of possible impact targets?

Thruster coordinates - pos/direction, maximum thrust rating?

ISP curves? (I think I can implement changing ISP within Orbiter, but I'd certainly like to get the the total dV capability correct, at least)

Accurate dry mass and fuel mass (for Centaur stage also).

I understand that the Centaur stage will purge it's excess fuel after TLI - how soon after launch does that happen?

ACS modes, firing sequences, manuever planning - especially timing of any planned course correction maneuvers. Any info about general attitude strategy would be of interest.

Trajectory data generally, but especially for the Lunar flyby. Any state-vector or SPICE files available to the public? (I'm waiting for the JPL Horizons data to be updated for the 17th June launch window!)

I can also help with the 3d models if you want to add more detail and get scaling correct (unfortunately the actual models are proprietary so I can't just give them out). I also have access to all the pictures taken of the spacecraft in various developmental stages as well. We launch LCROSS June 17th, and I would be happy to help out anyone interested in this very exciting unique mission.

I need to keep the model poly-count reasonably low so it doesn't impact on the Orbiter simulation frame-rate - but if you have any nice 3-views/design drawings of LCROSS, or accurate overall dimensions, that would be very useful - I'm in the process of modifying the model so it looks a bit more like the pictures I've seen of LCROSS stacked with LRO, etc.

OK, enough from me for now ;-) Thanks again.
Regards,
Brian

 

[Likeshadow]

LCROSS Details

Thanks, Happy to be here.

Responses to your questions inline in bold:
Thanks for taking the time to drop by and say hello, and also for the kind offer of information!

Yes please! All info you can provide will be gratefully received. Even if it's not immediately relevant to the simulation within Orbiter, there's plenty of folks here who will enjoy the extra insight into the mission.

Stuff I'd like to know (that I can think of right-now):

Launch window on the 17th June?
We are looking at three launch times on the 17th spaced 5 minutes apart, starting at 17-Jun-2009 19:51.00(UTC):

Preliminary selection of possible impact targets?
This changes on a daily basis as we get new information from ongoing studies and current lunar missions, but I believe crater Cabeus is primary (south pole region). We can change the impact site in flight if there is late breaking info from LRO for example as it goes through it's commissioning. Within reason, DV expenditure becomes prohibitive the later we course correct, but planning a final selection in the L+50day range. Impact Pole is pretty much determined at launch.

Thruster coordinates - pos/direction, maximum thrust rating?
8 attitude control thrusters, 1lbf (5N). Firing is 3 axis stabilied by firing pure torque quads, dv force is close to zero. DV is with 2 5lbf thrusters (22N).

ID Location (m) Orientation
X Y Z X Y Z
1 0.959 1.005 -0.963 -0.5000 0.5567 -0.6634
2 -0.080 1.005 -0.963 0.5000 0.5567 -0.6634
3 0.959 -1.005 0.963 -0.5000 -0.5567 0.6634
4 -0.080 -1.005 0.963 0.5000 -0.5567 0.6634
5 0.959 -1.005 -0.963 -0.5000 -0.5567 -0.6634
6 -0.080 -1.005 -0.963 0.5000 -0.5567 -0.6634
7 0.959 1.005 0.963 -0.5000 0.5567 0.6634
8 -0.080 1.005 0.963 0.5000 0.5567 0.6634

Here's some numbers for ACS thrusters and Torque when LCROSS is attached to Centaur. Odd thrusters are on the top, even on the bottom.

Control Torque and Force using 1 Lbf Thruster for Cruise Mode right after LRO Separation - Assuming 1 N Thrust LevelFiring
LogicControl Torque (Nm) Control Force (N)
Quad Tx Ty Tz Fx Fy Fz
1,2,3,4 -0.523 0.000 0.000 0.000 0.000 0.000
5,6,7,8 0.523 0.000 0.000 0.000 0.000 0.000
1,4,5,8 0.000 3.305 0.000 0.000 0.000 0.000
2,3,6,7 0.000 -3.305 0.000 0.000 0.000 0.000
1,4,6,7 0.000 0.000 3.167 0.000 0.000 0.000
2,3,5,8 0.000 0.000 -3.167 0.000 0.000 0.000

Detached config:
Control Torque and Force for Final Descent right after Upper Stage Separation -

1,2,3,4 -0.523 0.000 0.000 0.000 0.000 0.000
5,6,7,8 0.523 0.000 0.000 0.000 0.000 0.000
1,4,5,8 0.000 3.305 0.000 0.000 0.000 0.000
2,3,6,7 0.000 -3.305 0.000 0.000 0.000 0.000
1,4,6,7 0.000 0.000 3.167 0.000 0.000 0.000
2,3,5,8 0.000 0.000 -3.167 0.000 0.000 0.000

ISP curves? (I think I can implement changing ISP within Orbiter, but I'd certainly like to get the the total dV capability correct, at least)
Hard to put these curves in here, but it's basically around 80 for a completely cold catbed (monoprop hydrazine system). Steadily increases in ISP up to about 5% duty cycle where ISP would be in the 220 range.

Accurate dry mass and fuel mass (for Centaur stage also).
Fuel mass for LCROSS is 305.5Kg of Hydrazine, 4.8Kg of Nitrogen as pressurant (322psia at room temp). LCROSS Dry Mass=586Kg, Centaur=2308Kg

I understand that the Centaur stage will purge it's excess fuel after TLI - how soon after launch does that happen? It's actually a very complicated process, and goes through several blowdowns to purge the LO2 and LH2 tanks, the Helium pressurant, and their Hydrazine RCS system. They do a transverse spin to blow out fuel through the main RL-10 engine, do a propulsive vent (unfired) to produce about up to 50M/s in delta V for LCROSS injection (varies with time window and day), and fir their RCS system in a null burn to dump its last fuel. The also open the SVV to vent out remaining Helium thorugh the LH2 tank. Centaur will have about 30-35lbs of LO2 and a few punds of H2 and He left onboard that they can't get rid off. (which is actually a big potential issue with LCROSS).

ACS modes, firing sequences, manuever planning - especially timing of any planned course correction maneuvers. Any info about general attitude strategy would be of interest. There's 5 major modes for the ACS, a safe mode which spins about the Y axis (solar array is -Y), a Delta V mode (fires delta V thruster pair, holding a 0.5deg attitude), a Slew Mode (High gain and rate mode to move the vehicle around (holds a 1 degree deadband and allows rates to develop about 4 times greate than other modes), and a few Steller inertial Modes with varrying deadbands (10deg, 0.5deg, and 0.1deg). A 10 degree deadband is our typical mode, tighter deadbands are used for targeting accuracy to point the payload instruments for example during the impact phase.

Trajectory data generally, but especially for the Lunar flyby. Any state-vector or SPICE files available to the public? (I'm waiting for the JPL Horizons data to be updated for the 17th June launch window!)
Perhaps, I'll have to ask about this one, we have all the above plus .e files from STK. I'll see if I can release one. I can give you Periselene times, DV requirements, impact times, lunar distance and inclination angles for example without any problem if you would like those.


I need to keep the model poly-count reasonably low so it doesn't impact on the Orbiter simulation frame-rate - but if you have any nice 3-views/design drawings of LCROSS, or accurate overall dimensions, that would be very useful - I'm in the process of modifying the model so it looks a bit more like the pictures I've seen of LCROSS stacked with LRO, etc.
In general, the LCROSS Spacecraft is built around an ESPA Ring launch adapter, which is roughly a 5 foot diameter, and about 2 feet tall. The panels on LCROSS, are 2x3 feet roughly, and sit about 18 inches outside the ESPA Ring - so roughly the the spacecraft has an 8 foot diameter. The D1666, 1134 and C22 adapters, sep systems etc between LRO and LCROSS and Lcross and The Centaur are 30" approximately and these bolt onto the ESPA Ring. I can give you more if you need it, but that gives a general sense for the size.


OK, enough from me for now ;-) Thanks again.

No Problem, hope that helps.


Regards,
Brian

 

[Mafuskas]

Very interesting information! Thanks for the insight, Likeshadow.

 

[flying coffin]

I understand that the Centaur stage will purge it's excess fuel after TLI - how soon after launch does that happen? It's actually a very complicated process, and goes through several blowdowns to purge the LO2 and LH2 tanks, the Helium pressurant, and their Hydrazine RCS system. They do a transverse spin to blow out fuel through the main RL-10 engine, do a propulsive vent (unfired) to produce about up to 50M/s in delta V for LCROSS injection (varies with time window and day), and fir their RCS system in a null burn to dump its last fuel. The also open the SVV to vent out remaining Helium thorugh the LH2 tank. Centaur will have about 30-35lbs of LO2 and a few punds of H2 and He left onboard that they can't get rid off. (which is actually a big potential issue with LCROSS).

Do you know what the spin rate will be for the transverse spin?

I can give you Periselene times, DV requirements, impact times, lunar distance and inclination angles for example without any problem if you would like those.

Yes, Please!, and THANK YOU very much for all of this very useful information!

 

[BrianJ]

Fascinating! I wish the folks involved with the public-outreach for missions like LRO/LCROSS would go into a little bit more depth about stuff like this, on the websites.​

Just a few more questions:
What's the reference plane for the thruster coordinates - is it the spacecraft separation plane?​

The fuel purge procedure for the Centaur is interesting.
So, the RL-10 main engine is not reignited after the LRO injection burn? Could you give me any idea as to when the "transverse spin(fuel purge)" maneuver would happen? (I wonder if ground observers will be able to see a "doughnut" shaped cloud of fuel in the sky!? I know fuel purges from launcher stages can be seen occasionally)​

Cheers,
Brian​

 

[Likeshadow]

Do you know what the spin rate will be for the transverse spin?

[/B]Yes, Please!, and THANK YOU very much for all of this very useful information!

Yes, the Centaur Transverse spin will be at 1 deg/sec. During spin with LO2 and LH2 valves open, they will also be venting helium pressurant. Valves will stay open until pressurant bleeds down to about 400psia, at which point the pneumatic LO2 and LH2 valves (actually caled the OIV and FIV valves for Oxidizer Inlet Valve and Fuel Inlet Valve) will close since they require 400psi to keep open.

---------- Post added at 01:36 AM ---------- Previous post was at 01:15 AM ----------

Fascinating! I wish the folks involved with the public-outreach for missions like LRO/LCROSS would go into a little bit more depth about stuff like this, on the websites.​

Just a few more questions:
What's the reference plane for the thruster coordinates - is it the spacecraft separation plane?​

The fuel purge procedure for the Centaur is interesting.
So, the RL-10 main engine is not reignited after the LRO injection burn? Could you give me any idea as to when the "transverse spin(fuel purge)" maneuver would happen? (I wonder if ground observers will be able to see a "doughnut" shaped cloud of fuel in the sky!? I know fuel purges from launcher stages can be seen occasionally)​

Cheers,

Brian​

Good Question, I always thught it was the LRO/LCROSS Separation Plane, but now you have me thinking - it may be the top of the C22 adapter since the D1194 and D1666 adapters were the responsibility of ULA. I'll have to look this one up to be sure.

The RL-10 is not reignited after LRO Seperation (it is lit twice prior to LRO sep). The transverse spin occurs after a CCAM is done post LRO sep. The CCAM separates LCROSS from LRO more than a kilometer and then the Centaur begins the transverse spin, say about 30-40 minutes post LRO sep. LRO sep by the way occurs between 45 to 75 minutes post launch, depending on the launch window which will have either a short or long coast in Earth orbit. I have seen some pictures and ground observation of fuel purges as well, but to date I don't think ULA/Lockheed Martin have released them officially - there is some amateur stuff online. This will be the first time they've done the transverse spin with the Centaur, so from the right perspective you might actually be able to see donut or spiral effect.

 

[Likeshadow]

To answer the reference plane question, it is at the separation plane between LCROSS and the Centaur (X= 0). The separation location is between the D1666 Centaur adapter ring and the LCROSS ESPA Ring Adapter. From the top of the Centaur, you have a C22 adapter ring bolted to the D1666 adapter ring, the Separation clampband (CBOD system) then the LCROSS ESPA Ring adapter. At the top of LCROSS, you have a C22 adapter ring bolted to the B1194 adapter ring (white if you see any real photos of LCROSS) then another Separation clamband conntect to the LRO adapter ring. One thing I notice in the model views on this forum is that the adapter rings on top of LCROSS are not included. The C22 is is gold aluminum and the B1194 is painted white for thermal reasons.

 

[BrianJ]

To answer the reference plane question, it is at the separation plane between LCROSS and the Centaur (X= 0)

Yes, that figures. Thanks!

I've managed to implement more realistic pos/dir for LCROSS RCS thrusters, as well as an automatic "spin/fuel-purge" maneuver for the Centaur, along with an unlit mode for the Centaur main engine.

Also some changes to the Centaur, LCROSS and LRO models. Here's some screenies:

 

[BrianJ]

Only 10 days 'til launch!

Updated LRO/LCROSS add-on will be available soon.

In the meantime, here's a gratuitous screenie of my latest LCROSS trajectory, flown/recorded in Orbiter - displayed by Celestia.

 

[astrosammy]

Great to hear! Will it include in-Flight scenarios? That would be nice.

 

[BrianJ]

Great to hear! Will it include in-Flight scenarios? That would be nice.

Well, I tend not to include in-flight scenarios - for me, the fun is in getting there. But I guess I could include a flyby and a pre-impact scenario

 

[Likeshadow]

in-flight scenarios

Well, I tend not to include in-flight scenarios - for me, the fun is in getting there. But I guess I could include a flyby and a pre-impact scenario

The Lunar flyby scenario is actually quite complicated. About 1 hour post perisilene we manuever the +X to point and dwell on three sperate lunar surface targets for 5 minutes each (well measured surface areas that we use to calibrate the instruments). We then slew the +X to 3deg off the lunar limb, and slew six degrees back and forth across the limb three times, and then slew to another orthogonal limb location and do another limb crossing set. The lunar targets allow us to optomize the integration times being used for instruments, and the limb slews allow us to calculate the pointing angles of the instruments to a higher degree of accuracy than we can do with lasers on the ground (and also accounts for any launch vibration structural stress relaxation or vibrational movement).

I may be able to get an example .a and .e file for this if anyone is interested. I can also probably release an STK visualization if we can figure out how to post it where people can get to it.

As a note, LCROSS will do several calibration operations:
Starfield cal - point instruments at a star to calibrate boresights
Lunar swingby Cal - calibrate instrument integration times on known lunar surface targets and boresight angles to a high degree of accuracy with limb slews
Earthlook and Moonlook - Looking at the Earth or Moon, verify pointing accuracy and integration times, slew across the body several times in two axis to fine tune pointing further (mission has placeholders for 3 of these operations).

---------- Post added at 06:25 PM ---------- Previous post was at 05:36 PM ----------

Here's a a major event schedule for LCROSS this gets tuned for specific launch times, but forms the relative association of events:

LRO TLI (Pitch 180) Launch + 1-2 hrs
ACS Slew & DV Test TLI + 6 hrs
TCM1 = DV1 (1.2 m/s) TLI + 25hrs
TCM2 TCM1 + 1 day
TCM3 Swingby - 1 day
Swingby Cal Periselene + 1hr
Pitch Flip Pitch 0 (Ecliptic Normal)
TCM4a Swingby + ~2 days
TCM4b Swingby + ~7 days
Cold-Side Bake Roll 180
Pitch Flip Pitch 180 (Ecliptic anti-normal)
TCM5a=DV2 (19.4 m/s) (Swingby+7 days)-(Swingby + 50 days)
TCM5b DV2 + 5 days
Earth Cal #1+ Pitch Flip Pitch 0
TCM5c DV2 + half orbit
Thruster Cal (Cont.) Earth Point
Pitch Flip Pitch 180
Earth Cal #2 + Pitch Flip Pitch 0
TCM6 DV2 + 2 orbits
Moon Cal Moon Pointing (if needed in close orbit to moon)
TCM7 TCM8 - 5 days
TCM8 TCM9 - 5 days
Pitch Flip Pitch 180
TCM9 Impact - 3 days
TCM10 Impact - 11 hrs
Centaur Sep Impact -9 hrs
LCROSS Braking Burn Impact - 8hrs (4 min Centaur separation at impact)
LCROSS Slew to Impact Observation Impact -90 min

 

[BrianJ]

Hi Likeshadow,
thanks for the extra info - absolutely fascinating and a real eye-opener (for me anyway) as to the complexities of a mission like this. I was just reading the LCROSS Flight Directors blog http://wiki.nasa.gov/cm/blog/lcrossfdblog which is also very informative. Glad the FWR went well!

I may be able to get an example .a and .e file for this if anyone is interested. I can also probably release an STK visualization if we can figure out how to post it where people can get to it.

Pardon my ignorance, but what are .a and .e files? I'm interested to see, anyway! Sadly, I don't have STK - but I know a couple of folks who do, so anything you care to pass on is welcome. Are they large files? Anything smaller than 10Mb, you can email to me and I'll make available via my "utility" website. Larger than 10Mb - use the file-sharing website of your choice, or you could use www.orbithangar.com (the Orbiter resources repository), if it makes life easier I'm happy to give you my login/password for upload to OrbitHangar.

Pitch Flip Pitch 0 (Ecliptic Normal)

Is this the standard attitude during the cruise phase - x-axis orthogonal to the ecliptic (ecliptic normal or anti-normal)?

Thanks again for taking the time to pass on your knowledge about this mission - I know you must be extremely busy at the moment!

Best regards,
Brian

 

[Likeshadow]

Hi Likeshadow,
thanks for the extra info - absolutely fascinating and a real eye-opener (for me anyway) as to the complexities of a mission like this. I was just reading the LCROSS Flight Directors blog http://wiki.nasa.gov/cm/blog/lcrossfdblog which is also very informative. Glad the FWR went well!

Pardon my ignorance, but what are .a and .e files? I'm interested to see, anyway! Sadly, I don't have STK - but I know a couple of folks who do, so anything you care to pass on is welcome. Are they large files? Anything smaller than 10Mb, you can email to me and I'll make available via my "utility" website. Larger than 10Mb - use the file-sharing website of your choice, or you could use www.orbithangar.com (the Orbiter resources repository), if it makes life easier I'm happy to give you my login/password for upload to OrbitHangar.

Is this the standard attitude during the cruise phase - x-axis orthogonal to the ecliptic (ecliptic normal or anti-normal)?

Thanks again for taking the time to pass on your knowledge about this mission - I know you must be extremely busy at the moment!

Best regards,
Brian

Yes, most of the time we are ecliptic-normal or anti-normal. Our two omni antennas give us 4pi Steradian comm coverage, but where the two antennas overlap there is some RF interferometry going on. So when the earth angle reaches 90deg to the primary omni, we do a 180 pitch flip which reverses the angle progression to the Earth and the angle starts going down again.

There is no major reason for staying in ecliptic-normal or anti-nomal attitude, it just makes it easier from a manuever planning standpoint to use two reference positions that are well defined. However, we have sensitive instruments in +X that we want to keep away from the sun, these atitudes keep them 90degs away and we don't have to worry about violating our exclusion zones (sun in these optics will melt the fiber optic connectors to the spectrometers in under a 10th of a second).

.a and .e files are STK attitude and ephemeris files. We are using J2000 quaternions. If you have something that can ingest J2000 quaternions, there is nothing magical about these files. They are simple text files with time references and quaternions. They aren't very large.

Anyway, off to the cape in the morning (Friday)for final launch vehicle inspection. LCROSS and LRO are in final launch configuration. All safety locks are off and the LCROSS vehicle is waiting for discrete signals from the Centaur to wake up and take control of the stack after TLI. I should be as close as you are alowed to get for the shuttle launch Saturday morning also (our launch pad is right next to shuttles).

 

[flying coffin]

I now have AV020 in my current_reality.scn YeeHaw!:speakcool:

 

[Voyager_VI]

Brian,
Another home run, right out of the park!!! Well done

 

[2552]

Is the remaining dV in the Centaur supposed to go below 50m/s after the spin-purge, because it is at 43m/s now and dropping slowly.

---------- Post added at 10:29 PM ---------- Previous post was at 10:28 PM ----------

Even though it says "Spin/Purge finished"

 

[flying coffin]

It shouldn't be dropping unless you have an autopilot on.
The spin/purge shouldn't be happening yet. It actually happens
after the LTMFD TLICC burn at 25M alt. (yeah the docs are wrong about that)
You need about 25 m/s to target LCROSS