Chapman Challenge

[mbartley]

But I do really enjoy trying to minimize deltaV in trajectories. So to whatever extent I can enjoy these challenges just by taking part in the figuring out trajectories, I will. However, if it is going to at all be associated with the actual posted challenge, I would need to know the deltaV limits. So it would be really cool if the challenge posted the limits. Or maybe those that are familiar with the rockets could let me know what the limit is.

In my reading I've found earth escape performance graphs for some launch vehicles. For example, on page 3 of
http://www.spacex.com/Falcon9DataSheet.pdf (7 Megabytes)
and on page 135 of
http://www.ulalaunch.com/docs/product_sheet/Atlas_Mission_Planner_14161.pdf (warning 33 Megabytes!)
There are graphs of C3 vs payload mass for the Falcon 9 and Atlas V 401, respectively. By eyeballing these graphs, for the 1340 kg mass of Chapman, the Falcon 9 should yield a C3 of about 17 km^2 / s^2, and the Atlas V 401 should yield a C3 of about 43 km^2 / s^2.

If I understand the math, that would be hyperbolic escape speed of 4.1 km/s for Falcon 9 and 6.6 km/s for Atlas V 401. (and 10 km/s for Delta 4 Heavy, and 9 km/s for Atlas V 551) Is that what we need for planning in TransX or IMFD?

 

[tblaxland]

If I understand the math, that would be hyperbolic escape speed of 4.1 km/s for Falcon 9 and 6.6 km/s for Atlas V 401. (and 10 km/s for Delta 4 Heavy, and 9 km/s for Atlas V 551) Is that what we need for planning in TransX or IMFD?

Good research! I normally fly the vehicle in LEO to see what delta-v I can realistically achieve (I expect my flying is not quite as good as the real launch guidance!).

IIRC, the Chapman versions (Inner-1, Inner-2, Outer) have different masses so you need to check where you are heading first and select the appropriate version, then check its mass.

 

[Zachstar]

Any good addon that requires manual guidance or lacks access to thust/pitch data will give a little leeway. Call it a cheat if you will but last time I checked people like Flytandem are using TransX and not ten thousand dollar guidance computers.

Also with such as Delta IV heavy. The computers take into account FAR more than Orbiter can simulate. And will take any safe advantage to give that extra fuel leeway.

 

[flytandem]

In my reading I've found earth escape performance graphs for some launch vehicles. For example, on page 3 of
http://www.spacex.com/Falcon9DataSheet.pdf (7 Megabytes)
and on page 135 of
http://www.ulalaunch.com/docs/product_sheet/Atlas_Mission_Planner_14161.pdf (warning 33 Megabytes!)
There are graphs of C3 vs payload mass for the Falcon 9 and Atlas V 401, respectively. By eyeballing these graphs, for the 1340 kg mass of Chapman, the Falcon 9 should yield a C3 of about 17 km^2 / s^2, and the Atlas V 401 should yield a C3 of about 43 km^2 / s^2.

If I understand the math, that would be hyperbolic escape speed of 4.1 km/s for Falcon 9 and 6.6 km/s for Atlas V 401. (and 10 km/s for Delta 4 Heavy, and 9 km/s for Atlas V 551) Is that what we need for planning in TransX or IMFD?

Thanks. So there really is quite a choice. With even with just the Falcon at 4.1 km/s one could go anywhere in the solar system or even exit it altogether as it will provide the push to start the sling windup of the inner planets. The problem comes if you actually intend to stop at your destination wherever that may be. And if we are then limited to 2.97 km/s for the Chapman probe (from info I got earlier/ thanks tblaxland) to handle all the MCCs, deep space maneuvers or the destination orbit insert burn, we could very well have a tight budget.

Thanks again for the push for me to push the envelope. I recall how challenging it was to do my first sling. Eventually it was multiples or trying to use the inner's to get to Jupiter. But to do it with jupiter at an exact date and then to do it with minimal encounter speed.... well, there seem no end to the wonderful challenges in orbiter.

thanks everyone, and especially Martin!

 

[Piper]

...If I understand the math, that would be hyperbolic escape speed of 4.1 km/s for Falcon 9 and 6.6 km/s for Atlas V 401. (and 10 km/s for Delta 4 Heavy, and 9 km/s for Atlas V 551) Is that what we need for planning in TransX or IMFD?

Wow, I wish I could get it that good. I consider myself pretty good, but the range I've been typically able to get is:

Falcon 9: 2.7 to 3 km/s
Soyuz: 3.8 km/s
Atlas V 402 (I haven't tried the 401): 4km/s
Delta 4 Heavy: 10 km/s
Atlas V 552: 7 to 8 km/s

 

[mjanicki]

Ok, this is getting fun. I haven't done much orbiter work with launchers so I'm learning as I go. I want to work on the basic challenge #2 using the Chapman Inner and an Atlas V 422. To get ready for the challenge I decided to use a Mars insertion as a more familiar way to get used to the Atlas V.

My first few attempts were horrid. I couldn't even get a stable parking orbit with the Atlas. Once I got the hang of it though, I was able to get to Mars from LC41 without using any fuel from the probe. Two aerobrakes and a short burn later I had Mars orbit with 99.4% fuel in the probe. I was pretty happy.

But my ability to use the Atlas efficiently seems to need a lot of work. Right now I tend to reach my target altitude with nowhere near the velocity necessary to maintain LEO, so I have to burn far too much fuel just to get stable. Does anyone have any tips for a good launch profile for the Atlas V?

Thanks for any insights, and I'll work on the basic challenge tonight.

 

[Whatu]

I'm currently attempting the Venus challenge with an Ariane5 ECA.
Using the Inc and LAN given by transX, put that into LaunchMFD 1.2.8 (if it doesnt do anything, that ecliptical coordinates correspond to a eq. orbit with less inclination than your launch site)

Then LaunchMFD will give you a "point to aim" (pitch and heading) that should put you in LEO perfectly.

Note: At first, R.Inc as indicated by TransX 1st stage will be decreasing. When it stops decreasing, forget about the heading of LAunchMFD (but not the pitch) and steer to right or left to continue decreasing R.Inc)

At least, thats how I'm doing it now, and I could launch with just 0.09 R.Inc


And a few questions myself:

I have 98% fuel of the Ariane upper stage.
The manouvre shows aprox. 4000 m/s, but my fuel runs out when i have 200 m/s left... tblaxland wrote it had 4.5 km/s...

Can this be related to that I havent changed the "weight" in the ariane config? I left the default weight, how much does the chapman inner weight?

And another thing; I dont understand "Ej. Orientation" in TransX.. Why does my target orbit change, but no the overall plan... I just cant visualize it in my head, any help?

 

[T.Neo]

And another thing; I dont understand "Ej. Orientation" in TransX.. Why does my target orbit change, but no the overall plan... I just cant visualize it in my head, any help?

I don't use Ej. Orientation. I use that escape plan thing just to find out the rought time of departure.

 

[flytandem]

(snip)
Note: At first, R.Inc as indicated by TransX 1st stage will be decreasing. When it stops decreasing, forget about the heading of LAunchMFD (but not the pitch) and steer to right or left to continue decreasing R.Inc)

(snip)

And another thing; I dont understand "Ej. Orientation" in TransX.. Why does my target orbit change, but no the overall plan... I just cant visualize it in my head, any help?

Here's an excerpt from a post I made on the M6 forums...

I'll try to draw a verbal image to try and explain it. Hopefully you'll be able to follow along.


Imagine you are looking at a ball. Let's pretend this is the earth. Imagine that something is in orbit around this ball and is going to eject away from the earth directly away from you. There are lots of options to do this.

Let's label clock positions as a normal clock from your point of view of the ball.

Perhaps something in orbit around the ball is going away from you at the 12 o'clock down the far side as you're looking at it, toward you at the 6 o'clock and straight up the side you are looking at. This orbit would require the eject to be at about the 12 o'clock position while it's going away from you.

But something could also be going the opposite way around the ball and the eject position for this orbit would be at the 6 o'clock position also going away from you.

Or it could be going left to right on the near side to you coming toward you at the 9 o'clock position and away from you at the 3 o'clock position. This orbit would do the eject at the 3 o'clock position, when it's going away from you.

So there is in effect a full 360 degrees of choices for the "orientation" of the eject trajectory all of which provide the eject direction away from you as you look at the ball.

Now, if something is in orbit like the first example where it would eject away from you (the observer) at the 12 o'clock position. You could swing the eject orientation until it reads zero relative inclination. You see adjusting the orientation just takes the eject around the full 360 deg choice of eject options.

But not all orbits will get to zero by adjusting the inclination. For example what if something was going around the ball clockwise as you are looking at it. It is never going away from you. It goes right at 12 o'clock, down at 3, left at 6 and up at 9 o'clock. No matter how you swing the eject orientation it will always be fairly high relative inclination. It is never going away from you while doing its orbit.

What is the grey line? This is where the objects orbit is crossing the orbit of the eject trajectory.

So if you are already in orbit around the earth, you could swing the orientation to minimize the relative inclination then warp until you are approaching the grey line. Go AN and give it a test burn. If the rel inclination is increasing quickly go to DN for the burn. Burn until the line goes 90 degrees from you position. Then readjust the orientation to put the line over you, do another burn to swing it 90 etc etc. It will go to zero rel inc fairly quickly doing this.

If you are on the ground wanting to launch. Warp slowly ahead in time and also keep adjusting the orientation to put the grey line over or slightly ahead of you. When you see the launch heading becoming fairly easterly ( close to 90 is best if it will go that far) then launch. It's a bit of an art reducing the rel inc during the burn to orbit but you can always fine tune it once in orbit.

rob

ps: I do want to add that you are not required to adjust the ej orientation before launch with leaving it there after launch. Even while you are accelerating to orbit speed you are allowed to adjust the eject orientation. I usually wait till I am at least 1/3 orbital speed then I will adjust the ej orientation around to placing the white line just a tiny bit ahead of my position then yaw the ship to change plane to reduce the relative inclination. If swinging the ej orientation causes you to be close to 180 out then keep swinging the eject orientation a full 180 to get the other end of the white line over you. Having the view set to Plan is a good idea too.

Another tip: The MFD refresh rate in the Orbiter Launchpad Parameters is WAY too slow with the default 1 second value. I have it set to .01 seconds and TransX responds much nicer.

 

[Whatu]

Here's an excerpt from a post I made on the M6 forums...

(...)

Another tip: The MFD refresh rate in the Orbiter Launchpad Parameters is WAY too slow with the default 1 second value. I have it set to .01 seconds and TransX responds much nicer.

So, if I understand correctly, when I make a plan, it has a "direction to eject" (to where we are looking, in the ball example) and swinging Ej orientation changes the point in which we eject in that direction?

Anyways, its much clearer now, thank you very much

Btw, I think I saw that tip in one of your tutorials (probably) and it makes TransX another world. Thanks again!

 

[mbartley]

But my ability to use the Atlas efficiently seems to need a lot of work. Right now I tend to reach my target altitude with nowhere near the velocity necessary to maintain LEO, so I have to burn far too much fuel just to get stable. Does anyone have any tips for a good launch profile for the Atlas V?

I've mostly flown the Atlas V 401. My usual procedure is to fly straight up until vertical speed is 70 m/s. Then pitch over to 87 degrees. Then fly a "gravity turn" until 1st stage cutoff. After 2nd stage ignition, fly to the PEG flight director in LaunchMFD. IIRC this also works for Delta 4 Heavy.

For other launch vehicles, you usually have change the time and amount of the initial pitchover. Generally the faster the launch vehicle accellerates off the pad, the sooner and/or further the initial pitchover. I have to trial-and-error this and make notes to myself once I've found a combination that works OK.

 

[tblaxland]

I have 98% fuel of the Ariane upper stage.
The manouvre shows aprox. 4000 m/s, but my fuel runs out when i have 200 m/s left... tblaxland wrote it had 4.5 km/s...

Can this be related to that I havent changed the "weight" in the ariane config? I left the default weight, how much does the chapman inner weight?

Good question! I just checked and noticed a discrepancy in the original config files from Piper. The Chapman Inner 1 (what you would use for the Venus challenge) weighs 1340kg fully fuelled (800kg fuel + 540kg dry mass) according to its config file. The configs for the launch vehicles have the payload weight listed as 1240kg though. I used 1240kg because I had copied the data from Piper's configs without checking. We really should be using 1340kg. All the configs I checked have this 100kg error. I'm assuming it was just a simple maths error.

The Ariane 5 ECA default payload weighs 2600kg. That should account for the difference in dV.

 

[Piper]

Good question! I just checked and noticed a discrepancy in the original config files from Piper. The Chapman Inner 1 (what you would use for the Venus challenge) weighs 1340kg fully fuelled (800kg fuel + 540kg dry mass) according to its config file. The configs for the launch vehicles have the payload weight listed as 1240kg though. I used 1240kg because I had copied the data from Piper's configs without checking. We really should be using 1340kg. All the configs I checked have this 100kg error. I'm assuming it was just a simple maths error.

The Ariane 5 ECA default payload weighs 2600kg. That should account for the difference in dV.

Oops, your right, all the weights are off. I was playing around a lot with the weights towards the end of developing the Chapman probes, trying to make the weight and fuel levels realistic, without making it too heavy. I must of increased the weights in the config files, and forgot to repeat it in the scenario and multistage2 files. I guess I'll be releasing an update this weekend.

 

[mjanicki]

Many thanks to mbartley for your suggestions for the Atlas V. I used those tips and a good bit of trial and error to get, not perfect but, a usable launch for the basic Venus mission.

So, my report for Chapman Challenge #2 Basic

Probe: Chapman Inner-1
Launcher: Atlas V 401
Planner: IMFD

Launch: 13 Nov 2013 from LC41
Arrival: 01 Mar 2014 just before midnight of 02 Mar

No Launch MFD, just IMFD surface launch program.

One is probably not supposed to, but I carried stage 2 and the fairings until after the final aerobrake maneuver. That might not be the right thing to do, but since it still had plenty of fuel I didn't want to let it go.

Ejection burn required just under 4k dV but with an off-plane course there was no need for a plane change so I didn't think 4k would be a problem.

One course correction of ~200 dV on 11 Jan 2014. Stage 2 still had 6.4% fuel load after this burn.

One burn once inside the SOI of Venus using IMFD Planet Approach to set PeA for first aerobrake. This left Stage 2 with 4.2% fuel load.

Five aerobraking maneuvers between initial intercept and the evening of 02 Mar 2014 with little fuel expenditure -- just enough to raise or lower PeA for the next aerobrake. I don't have Aerobrake MFD so I licked my finger and stuck it out the window to get an idea of what PeA I should use for the first aerobrake. I set it a bit higher than I thought it should be since I was approaching Venus with eccentricity of only 1.2 and had enough fuel left in stage 2 to burn retrograde for capture if the initial aerobrake didn't work. Then I just raised PeA a bit to be safe for another pass and eventually got Ecc down to 0.05 with ApA 785k after the fifth aerobrake.

One final burn from stage 2 was used to raise PeA then I jettisoned the probe and made final translational burns to circularize the probe's orbit at an altitude of 780k.

This was a nice challenge. I learned quite a few new things in Orbiter that I hadn't tried before.

Pics are first aerobrake, final orbit interior, final orbit exterior.

 

[atuhalpa]

D4HV

Piper, I have been experimenting with almost all the launch rigs and I have a problem with D4HV EDS. After my initial burn out of LEO I leave the earths SOI and even though I have 24.1 % fuel left Rotation doesn't respond only translation. Any thoughts?

Atuhalpa

 

[Piper]

Piper, I have been experimenting with almost all the launch rigs and I have a problem with D4HV EDS. After my initial burn out of LEO I leave the earths SOI and even though I have 24.1 % fuel left Rotation doesn't respond only translation. Any thoughts?

Atuhalpa

The fuel in the DIVH upper stage is cryogenic, which means in reality that it boils away if not kept actively cooled. The DIVH in orbiter simulates this by cutting out your thrusters and engine after a certain length of time (I'm not sure how long that is, but it's not very long).

 

[atuhalpa]

Challenge Questions

Piper, I have finally after many trials with many launch engines achieved a highly eliptical (Pea 29.38M, Apa 405.5M) orbit of venus by aerobraking at 104.5 k altitude. I don't know if the aero dynamic effects of the solar panels and antenna boom are modeled but it seemed that the probe was much more stable when they were retracted. Unfortunately I have NO Dv left at all whatsoever as I used the last of it attempting to circularize my orbit as much as possible. My question is (if it is not asking too much) In your experience with this scenario, What is a reasonable amount of Dv to have in reserve after achieving orbit around Venus? I used Soyuz with fregat and I launched from Kourou.

Atuhalpa.

( I found out I don't know as much about Orbiter as I thought I did!)

 

[Piper]

Piper, I have finally after many trials with many launch engines achieved a highly eliptical (Pea 29.38M, Apa 405.5M) orbit of venus by aerobraking at 104.5 k altitude. I don't know if the aero dynamic effects of the solar panels and antenna boom are modeled but it seemed that the probe was much more stable when they were retracted. Unfortunately I have NO Dv left at all whatsoever as I used the last of it attempting to circularize my orbit as much as possible. My question is (if it is not asking too much) In your experience with this scenario, What is a reasonable amount of Dv to have in reserve after achieving orbit around Venus? I used Soyuz with fregat and I launched from Kourou.

Atuhalpa.

( I found out I don't know as much about Orbiter as I thought I did!)

I find its best to use just enough to get yourself into orbit (and a little bit more), and then let aerobraking do the rest.

 

[astrosammy]

I've completed the Venus challenge, see my blog for informations.
http://orbiter-forum.com/blog.php?u=694&blogcategoryid=7

 

[T.Neo]

Wow, astrosammy, you used a space shuttle to launch, I would have used any old launcher. :speakcool:

Did you reenter and land the shuttle?