Lunar Mission Sim

[CraigD]

Anyone who would like to can run XGRAVSIM4.

In order to do so, you’ll need a MUMPS language interpreter. A free, non-expiring, single user copy of the one I use can be had at Free Caché Downloads. The vendor, Intersystems, requires you register an email address with them to get it, but in my experience won’t spam you unless you request it, or give the address to any other company.

Pay no attention to the name “Cache”. Intersystems makes a great effort to hide the fact that Cache is, in fact, a (much extended) implementation of the MUMPS language, but it’s one of the best.

Once installed, you need only click on the icon it installs in your system tray, or follow the start menu path to its “Terminal” application, and paste the following into it

 f  r R q:'(R)  s I=((R,";",(R,";")),":") i (I) s @I=R

(making sure to end with exactly 1 Enter keystroke) followed by the “MUMPS code for XGRAVSIM4” in post #6, followed by a blank line (the Enter key), followed by

x XGRAVSIM4

. For documentation, enter ? at the XGRAVSIM4> prompt.

You can then paste any of the command lines in my examples above into it to run it, or make up your own.

To do anything but manually adjust the acceleration of bodies, you’ll need .X property code, which you must know MUMPS to write. Post #6 has a little .X program that allows you to set a specific impulse of the motor (ship.X(“SI”)) the empty (no propellant) mass of the ship (ship.X(“M0”)) and a propellant flow rate (ship.X("Mf")) which can be pasted into the sim to see how simple rockets in a vacuum would behave. Note that in my example, I forgot to multiply the SI of 250 seconds by 9.8 m/s/s, so my 1000 kg rocket is under-powered by a factor of nearly 10 vs. a real solid fuel rocket – though it still flys

A nice feature of XGRAVSIM4 is that you can enter $.all to output the “all simulation data” property, which is all the properties necessary to run the sim. These can easily be copied and pasted into text files, then pasted into the simulator with slight changes to run another simulation – just note that all output starts with a # comment character, which must be removed before pasting it actually does anything, and any line wrapping must be fixed manually (or avoided by capturing the text using File, Log in Terminal, or something similar)

[Janus]

Okay, here's a demo of a moon-shot with orbiter :


It shows my simple mesh of the lander on a intersect orbit with the Moon's surface. I started with 1850kg in LEO and used the spec for an off-the shelf booster to reach transfer velocity. It required a small course correction mid-flight to make the intercept.

The top information screen shows the oribtal information.
In order from top to bottom are:

semi-major axis
semi-minor axis
periapis distance
apoapis dist.
radial distance (at this instant)
eccentricity
period
time to periapis
time to apoapis
velocity
inclination
longitude of accending node
longitude of descending node
argument of periapis
true anamoly
true longitude
mean anamoly
mean longitude.

at the bottom next to the G is the G-field contribution.

The graphic shows the orbit in green. (the moon is the white circle)
The green line traces out the present radius vector.
The dotted line joins the nodes of inclination. Solid sqaure is the ascending node and the hollow square the descending.

Solid circle marks the periapis and hollow circle the apoapis.

You can add a second "target" orbit which will be shown in yellow, with its parameters down the right side.



The bottom display give readings relative to the Moon surface and contains the info you would use to make a soft landing.

It contains: an
artificial horizon
heading indicator.
ground speed (GS)
altitude (ALT)
vertical speed(VS)
pitch (PTCH)
bank (BNK)
Acceleration indicator (ACC)
Atmoshperic date (not applicable here)
Equalaterial postion and rate (EQU POS)
angle of attack(A0A)
vertical Acceleration (VACC)

These are just a couple of the information displays that can be brought up.

I had a little trouble creating the custom spaceship at first. Even following the docs anf tutorials step by step, the program crashed every time I launched it.

I finally resorted to hijacking an existing ship (satellite actually), and plugged my mesh and parameters in. The program accepted that. Hopefully, making use of the multistage settings won't cause the same problems.

[TheBigDog]

Fantastic Janus! Incredible. I am glad I spent the weekend working on my program, it was very educational. It seems somehow insignificant now - like I was rubbing two sticks together and you showed up with fireworks and an acetylene torch.

So, graphics aside, have you worked out the mission profile for a direct trajectory? If you can post a video of the mission that would be spectacular.

Bill

[Janus]

So, graphics aside, have you worked out the mission profile for a direct trajectory? If you can post a video of the mission that would be spectacular.

Bill

As of this point, It's a Ranger mission style hard impact trajectory. It will take some tweaking to simulate a soft landing. I could do it with the present set up by adjusting the fuel levels, but it wouldn't be realistic, as it would be using the same engine for trajectory boost as landing, and typically you would use separate engines for these tasks and discard the booster.

There is a flight recorder for the sim, that I should be able to use to create a video file.

[Janus]

I've made some progress with the orbiter sim. I can now create new ships without hijacking another ship's config file. This gives me a lot more flexibility. For instance, I can now simulate a transfer booster-lander combination and jettison the booster after it's exhausted.

Here are some screenshots of what I've gotten so far. Clockwise from the upper left are:
The booster-lander package.
The package with the booster firing.
Just after the jettisoning of the booster stage.
Some time after the separation of the Booster and lander.



I've gotten pretty good at hitting the moon, and am now working on the soft landing stage of the mission.

Iv'e also been working on a method of producing a demo video, but so far the resuts haven't be very good. The results are choppy, and the quality isn't that good due to having to keep the image size down.

For the best results quality-wise, it is best viewed from the Orbiter program itself. It can be downloaded as freeware. I can then provide all the files needed to run the lander sim. Just put them in the right folders and run it. One of the advantages of this is that the person playing back the sim can change viewing perspective, and even bring up different information displays as the sim plays back.

[TheBigDog]

I loaded and ran Orbiter on my PC last night... I had almost forgotten what the Blue Screen of Death looked like. I am going to try it on another PC, otherwise I will only be a spectator.

Bill

[Janus]

Okay, After quite a bit of fine tuning and adjustment I've come up with a video of the Lunar sim. It doesn't cover the actual soft landing, ( I'll do a second video for that) as youtube has a 10 min video limit, and I can't quite squeeze the whole mission into that short a time.

Of course, some of this video is time compressed, otherwise I would have a video that lasts for several days. Other parts of the sim run at real time, and certain parts run at 1/10 speed. The reason for this is that in order to get the video, I had to essentially record my computer screen with a digital camera while I actually ran the sim. Since certain points of the mission are very time sensitive, and some events have to be manually initiated, I had to slow things down, to get the timing right.

There are two information displays at the bottom of the screen, which change function as the sim progresses. At the start the left display shows the oribt with respect to the Earth and the right is a transfer tool that aids in timing the transfer boost. After the boost ends the right display is changed to show the craft's trajectory with respect to the Moon. On approach to the Moon the left display changes to the type of info needed to plot the landing; Altitude, vertical and ground speed, an artificial horizon, etc.

That's about it so here's the video, You'll probably have to turn the volume up to the hear the audio, it recorded a little on the low side.

YouTube - Lunar lander sim 1

[TheBigDog]

Fantastic Janus! Absolutely fantastic!

[CraigD]

Wow!

Is the Strauss soundtrack a feature of Orbiter, or something you added, Janus. In either case, a nice touch.

I didn’t notice any mid-course correction maneuver. Was this because there was none, or was it unnoticed due to the time compression? I recall from some of the Apollo data I’ve been using that, given the precision available to even modern spacecraft, a mid-course correction is a practical necessity.

So, to save me the labor (and test of my practical orbital mechanical skill ) of calculating them myself, can the Orbiter run produce a thrusts data (time, magnitude, and vector) in a simple text format. I’d like to plug it into XGRAVSIM4 and see how it works. And, of course, the data must be available in a form that can be used to actually program the control system of a spacecraft.

Given that there are so many science and commercial satellites performing routine orbital maneuvers, there must be some standards for this sort of control data. Is anyone familiar with them?

[TheBigDog]

Originally Posted by CraigD

Wow!

Is the Strauss soundtrack a feature of Orbiter, or something you added, Janus. In either case, a nice touch.

I didn’t notice any mid-course correction maneuver. Was this because there was none, or was it unnoticed due to the time compression? I recall from some of the Apollo data I’ve been using that, given the precision available to even modern spacecraft, a mid-course correction is a practical necessity.

So, to save me the labor (and test of my practical orbital mechanical skill ) of calculating them myself, can the Orbiter run produce a thrusts data (time, magnitude, and vector) in a simple text format. I’d like to plug it into XGRAVSIM4 and see how it works. And, of course, the data must be available in a form that can be used to actually program the control system of a spacecraft.

Given that there are so many science and commercial satellites performing routine orbital maneuvers, there must be some standards for this sort of control data. Is nayone familiar with them?

Since we are not trying to enter lunar orbit I would guess that a mid course correction might not be needed. The proper alignment for entering lunar orbit is much narrower than for hitting the moon close to the middle.

In watching the video I could not tell how the sim was accounting for the transition from earth to lunar gravity. I was playing one of the games someone had posted a couple on months ago last night, the gravity pods game. I am hoping that the sim I built will eventually work something like that, only on a much grander scale. I will leave it to the experts to do the realistic sims, and give us an idea of the launch windows we should be looking at for optimum payload delivery.

I loved the Strauss touch too.

Bill