TransX Moon-Earth Return - Need Help Understanding TransX

[LTrotsky]

I have a sort of related question, and I'm sorry if I'm thread-jacking here, but why not use IMFD for this? I'm an Orbiter newbie, but was able to set up a direct re-entry to Earth from lunar orbit and land deadstick at CSSC with an XR2 using IMFD pretty simply. What advantages does TransX have?

Threads are more interesting when "jacked" according to the needs of the community. :tiphat:

Your post brings up several related issues for me.

1. There's a boatload of add-on MFDs. I used TransX because it was part of the default Orbiter2010 package. Have I mentioned I'm new? Because of Blixel's video of the progression of my situation, I noticed that he was using BurnTimeMFD, for example. The issue is this : what is the best set of add-on MFDs for a beginner? I was looking at GlideScope, BurnTime, and the one which is specific for Earth-Moon transits (both ways, forgot the name of it). But there are a host of other MFDs and was just wondering what are those most useful for a person learning the ropes. My major issues right now are getting the basic mechanics down, learning fuel discipline, landing, and planning missions with defined success criteria.

2. The XR2. Maybe I missed something here but this ship doesn't appear to be in the default Orbiter. Naturally, thanks to this wonderful community, there are dozens of ships out there to incorporate into one's Orbiter install. I've seen David Coutney's videos in which he is using a multi-stage rocket, as well as an advanced ship that allows for custom loadouts (additional fuel, oxygen, etc). I've even seen beer cargo add-ons, but other than simulating an enhancing of the general enjoyment of space - which works especially well I would imagine if supplemented by real beer when working the simulation - I'm not sure how to incorporate this into my Orbiter install. The issue is this : what are some additional ships I should at least have installed and start familiarizing myself with if I am interested in near-future realism? (i.e., I probably won't be installing any Babylon5 ships).

---------- Post added at 03:50 PM ---------- Previous post was at 03:47 PM ----------

Well its not really possible to break a DG, but Congrats!!! :10sign::11sign:

I remember my first flight around the moon well:

http://www.orbiter-forum.com/blog.php?b=1261

Also, I should mention on my last two DG landing practices, fully manual I should add, the elevators were ripped off and I crashed, so it *is* possible to break parts of the DG off.

 

[Ripley]

Well, XR Fleet is a must IMHO.
Get it at Altea Aerospace: http://www.alteaaerospace.com/


MFDS:

GlideScope (you meant GlideSlope?), BurnTime, etc, are quite advanced MFDs.
If you feel comfortable with them, well...use them.

I would not leave IMFD, AerobrakeMFD, BaseSyncMFD, LTMFD, LaunchMFD (and its HUDDrawer companion) out of my personal bunch.
Phew, there are just so many out there...

About that two-way Earth-Moon MFD: maybe you were thinking of LunarTransferMFD, available at http://users.kymp.net/p501474a/Orbiter/Orbiter.html (home to another couple of already named MFDs)

 

[Shifty]

I'm a newbie as well, so take what I say with a grain of salt, but I like the XR2 because it's relatively easy to learn to fly it, but still complex and challenging to fly. It's got a great instrumentation layout; you rarely need to look at anything but the main panel, and the custom sounds are better than any other ship I've sampled. I like the DG-IV too, but its panels aren't as well laid out, nor does it have scramjets What sold me on the XR2 was the playbacks on the KSC to Wideawake challenge forum; incredible flying there:
http://www.orbiter-forum.com/showthread.php?t=32000

I've loaded a bunch of MFDs into my installation to try them out, but I find myself mostly only using IMFD, LTMFD, AerobrakeMFD, BaseSyncMFD and RendezvousMFD for normal (non-Shuttle) flights.

 

[LTrotsky]

Made Some Progress Understanding TransX

I've made some progress understanding TransX.

The key (for me) is understanding that a transit has specific stages, and that within each stage are different views, and within each view are different variables. It's like a 3 layer cake. In addition, some things which could be changed or adjusted don't show up unless you turn on "advanced" or turn a mode (like manuver mode) on.

So, armed with this understanding, which has slowly developed (read the TransX manual again, that helps), I attempted to go to Mars today in your standard DG. Thought it would be easy. It's not.

1. Getting plane aligned with Mars. Turns out to be painfully difficult. The reason is you have to first circularize your orbit, and then start planning the route. While you are doing that, if your orbit isn't perfect, which they never are, you start to fall out of plane. For a trip to the moon a degree off plane is not a big deal in a DG. For a trip to mars, .01 degree off plane can mean you miss. Hello Jupiter, or Mr. Sun.

2. It turns out that if Earth and Mars aren't in their optimal places for an Earth-Mars transit, it can take a long time and a lot of fuel to get there. Like, a year. Naturally, I didn't plan anything. I just hopped in the DG from the latest state and decided while in a high orbit to see if I could stage a trip to Mars. Earth and Mars were probably in the worst relative positions for this enterprise - Mars was at about 90 degrees behind Earth their sun orbits. Bad. When you prograde to intersect with Mars, you get to the Martian orbital path even further ahead of the target than you started out - Mars is moving a lot slower around in it's orbit than Earth is. If you try to prograde directly towards Mars when these are the relative positions, you have to cancel out all the velocity you have simply by being in Earth's SOI during its orbit around the sun. Which means in effect you really cant do it.

3. So the solution here, I thought, was to go prograde to the Mars orbit path, and much beyond it on a free return trajectory. While I was "TransMartian" I would be going much slower than Mars in an elliptical orbit around the sun that eventually would come back to Earth. When I recrossed the Martian orbital path, Mars would have caught up to me, and there could be an encounter. Long story short, intersecting the target involved another burn manuver after transiting the Mars orbital path, extending the ellipsis, and allowing a "catch up". When I recrossed the Mars path, the encounter showed I would be near.

4. Once you get the encounter down to within around 40k km (40m) you can play with plane change, outward velocity, prograde velocity, and the time to commence the burn - in very small increments, and get a nice encounter down to about 4000km. Nearer than this is really pointless with TransX since there are too many things that can and do change. That's what the update base orbits button is for in TransX.

5. So, all went well until I got close to the second manuver - the one where I am transiting the Mars orbital path with Mars about 90m kilometers behind me. I was lining up for the burn using translation, and had time accell on. Oops. Never do that. Ran out of RCS fuel. In the DG you can't crossfeed, either. So, no way to manuver anymore.

Anyway it was fun planning the first trip and getting out there. I think I would have gotton a good pass if I hadn't effed up on the attitude control fuel. Next time I will plan the trip when Earth and Mars are in better positions.

 

[Mister Mxyzptlk]

You must use the proper date for a Hohmann transfer launch window to start. Then you must launch into the correct plane of alignment. You use launch mfd and align while climbing to orbit. Once you have launched into the correctly aligned orbit you have made things a whole lot easier. Going to Mars is a whole quantum leap more complex than going to the moon.

 

[Ripley]

Congrats for the experiment, but there is an easier method.

These are the Hohmann transfer dates for a Earth --> Mars trip.
Adjust your scenario MJD to one of these:
http://clowder.net/hop/railroad/EMa.htm

Use the Date.exe utility you'll find in your_orbiter_root\Utils folder

 

[LTrotsky]

Going to Mars is a whole quantum leap more complex than going to the moon.

I posted the story to elicit comments like yours, which I believe help the community. Part of the appeal of Orbiter is the progressive challenge of the varied types of missions.

I am stab testing the sim atm, putting in add-ons only after I can determine their app impact and cross-compatibility. I have a whole list of add-ons that I want to add(launchMFD being one of them). It does require some serious mission planning to do almost anything outside the Earth's SOI. While doing things within Earth's SOI it is nevertheless important to learn the concepts. The idea of using part of the energy from the launch to align plane with target is a great efficiency. For example, without add-ons one can use map and align plane MFDs while launching to at least minimize the amount of burn one has to do for a plane alignment. Also, for a lunar transit, one can use the map and visually see when the moon's plane is fairly closely aligned with an orbit established from a KSC launch.

I was wondering if virtually all spaceflight can be considered a "transfer orbit".




---------- Post added at 12:35 PM ---------- Previous post was at 12:34 PM ----------

Congrats for the experiment, but there is an easier method.

These are the Hohmann transfer dates for a Earth --> Mars trip.
Adjust your scenario MJD to one of these:
http://clowder.net/hop/railroad/EMa.htm

Use the Date.exe utility you'll find in your_orbiter_root\Utils folder

I wonder why I didn't know about the date.exe utility.

I answered my own wonder : because on my Orbiter todo list was to ask the community how to figure out optimal launch dates, and hadn't done that yet because I'm still stability testing. I figured there was a site or app for that. So I didn't need to do date conversion yet. The site you referenced is now in my notes.

Incidentally there's a bunch of really interesting stuff on the parent of that website, including art. Is hop still around?

http://clowder.net/hop/railroad/sched.html

 

[LTrotsky]

Getting Better

Today I attempted a serious Mars transit.

Using the HTO dates provided above, I decided to launch 1 day ahead of the launch window day, in order to have enough time to align and stabilize the orbit. Loaded the Launch MFD and associated SDK. Using the LaunchMFD saved about 300kg of fuel over previous process.

The TransX plan involved 3 stages: Escape, Eject, and Encounter.

The Escape stage was set up to get within 20M (20,000 km) of Mars. The Eject and Encounter stages propagated automatically. Scheduled actual escape burn for the following day. During that time, I fiddled with TransX, attempting to get a closer approach, but whenever I hit base updates, the numbers were thrown. This is because, I think, that TransX will re-calculate the trajectory based on the current orbits of the bodies. It does not appear to project what the vessel orbit will be at the time of the burn - and this does change due to peturbations and other factors. (I have the peturbations box checked and I know that Orbiter models Earth's non-spherical gravity).

So the process was: re-circ the orbit every few hours, re-do the Escape Plan, re-align, and so on. As I got to within 2.5k/sec of launch, the approach distance seemed fairly stable with the Dv entered into the vectors. (Edit Note : it was during these orbital maneuvers and tweaking TransX that I noticed my escape trajectory would most likely dip very far down towards Earth. I was at about 230km orbit, so I raised the orbit to 900km - and recirced and aligned). As I got very close to the burn, alterations plane change and outward had much less effect than before, and base updates reported little change in the projected approach distance.

The Escape burn went off okay. I did a couple of course corrections at about midpoint and 3/4s. By this time the TransX Eject stage had disappeared, so turned on Maneuver mode in the Eject stage, which up until this point had no Dv set. With a couple small correction, the target distance PeA went down to about 100km. Thought this was close enough, and didn't want to hit the planet either. Also wanted to lower the capture Dv.

It was a thrill to see Mars getting closer and closer. I set the visual aid to planetarium, and at about 1 million km Phobos and Deimos propagated in that view as well. At this point Mars was exerting 0.02g on the vessel.

Everything looked on track. PeA, LAN, PeA Lat/Lon, and Inc all looked nominal.

I was getting set to perform another very minor burn to fine tune the approach when the application crashed. I believe I was at about 800km from the target. The crash reminded my of a long (in terms of continuous time running) session in which I was returning to the Earth from the Moon and was entering Earth's SOI at the point where the prograde button works.

So the crash was disappointing, after all the work. I have a playback which appears to capture all the data up to about 1minute before the application crash.

I am not sure what's causing these CTDs. It's the base game, plus a 5 texture packages (all the major planets, plus the Earth and Moon - all the latest available). I haven't even installed Orbiter Sound, or any additional ships. In addition, for this session, I added LaunchMFD and the required SDK.

Edit : I've been playing with my video card settings (AMD Engine Control Center), and have discovered that with some settings Orbiter crashes on launch, or hangs during launch. Possible some settings that can minimize CTDs.

 

[dacamp66]

I cannot recommend too highly Bruce Irving's (flyingsinger) e-textbook "Go Play In Space" it assumes you know nothing about space travel and goes into not only the "what to do" and "how" but also the "why you do it" aspects. it is widely considered to be required reading for any serious orbitnaut. it should solve many of your problems or at least enable you to "brain sweat" your way out of them.

Linky: http://www.aovi93.dsl.pipex.com/play_in_space.htm

 

[LTrotsky]

I cannot recommend too highly Bruce Irving's (flyingsinger) e-textbook "Go Play In Space" it assumes you know nothing about space travel and goes into not only the "what to do" and "how" but also the "why you do it" aspects. it is widely considered to be required reading for any serious orbitnaut. it should solve many of your problems or at least enable you to "brain sweat" your way out of them.

Linky: http://www.aovi93.dsl.pipex.com/play_in_space.htm

Yes. I have that already, but :embarrassed: haven't read it yet. Too jazzed about going to Mars which, if I can do, then Neptune's the limit (I guess).

Also looked at Celestia, which is like a galactic sandbox. They are in the process of adding ships, but not clear whether or not they have or ever will accurate grav mechanics.

Linkage : http://www.shatters.net/celestia/