Author Topic: SLS Trajectory Simulations  (Read 88294 times)

Offline quanthasaquality

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Re: SLS Trajectory Simulations
« Reply #140 on: 03/03/2014 01:35 pm »
One tradeoff though is that if you accelerate faster in the lower atmosphere, you run into higher dynamic pressures, making aborts harder. That said, Orion's LAS was sized based on outrunning "the Corndog", which had probably the worst max-Q I've ever seen for a proposed human launcher, so maybe it won't matter.

A forum search shows the Ares I nickname, 'the stick', to be more popular than, 'the corndog'.

Offline newpylong

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Re: SLS Trajectory Simulations
« Reply #141 on: 03/03/2014 02:21 pm »
But nowhere near as funny.

Offline quanthasaquality

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Re: SLS Trajectory Simulations
« Reply #142 on: 03/03/2014 02:57 pm »
Looking at the Direct 241 Heavy presentation baseball card, the 5 segment boosters only have to lift 1000 tons, for the core, second stage, and payload. The presentation baseball card also says a nice 118 tons to LEO. The SLS first stage core alone is about 1100 tons. The Direct 241 Heavy uses 4 ssmes, a shorter core, and 1 J-2X.

Given that 120 to 150 ton was the middle range of the payloads in the RAC 2 study, I presume that KBH and Bill Nelson wanted a bigger rocket. Add the 130 ton requirement, I bet KBH and Bill Nelson wanted the biggest shuttle derived rocket that would fit into the VAB. Bill Nelson calls the SLS a 'monster rocket'. Maybe a ~7 segment booster is what they'd really like, but the ground won't support 2 1000 ton solid rocket boosters. According to Steve's calcs, Pyrios has about 1.4 times the total thrust of the 5 segment booster...

Offline Steven Pietrobon

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Re: SLS Trajectory Simulations
« Reply #143 on: 03/04/2014 04:27 am »
According to Steve's calcs, Pyrios has about 1.4 times the total thrust of the 5 segment booster...

I'm not sure where you got those numbers. I have each RSRMV with 15.6 MN sea level thrust, compared to 16.1 MN with Pyrios (2xF-1B). That's only a 3% increase.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline sdsds

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Re: SLS Trajectory Simulations
« Reply #144 on: 03/04/2014 05:11 am »
I want to start by saying I believe trajectory simulation is the best approach to payload approximation, and give huge thanks to Steven Pietrobon for pursuing this.

That said, it makes sense to attempt to confirm simulation results via completely independent methods, and I chose the Schilling's Method calculator at http://www.silverbirdastronautics.com/ to attempt that for the SLS1C6J2 design. Attached for your amusement are images of my inputs and the result.

I tried to more or less faithfully convey to Schilling's the values from the pdf in
http://www.sworld.com.au/steven/space/sls/sls1c6j2.zip
doing appropriate units conversions, summing, etc.
— 𝐬𝐝𝐒𝐝𝐬 —

Offline Steven Pietrobon

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Re: SLS Trajectory Simulations
« Reply #145 on: 03/04/2014 06:18 am »
That's great sdsds! Thanks very much for doing that. We can see that my value of 133 t is 8 t or 6% higher than what that program gave. Its well within the 95% confidence range of 103 t to 152 t.

I found your page and made a number of corrections:

http://www.silverbirdastronautics.com/LVperform.html

Your Isp values are a little high. I believe this is because you used g = 9.8 m/s² instead of the international standard value of 9.80665 m/s².

For the first stage dry mass, I added the 9257 kg interstage mass and from the second stage the ullage motor dry mass of 201 kg and ullage motor propellent of 218 kg.

For the second stage dry mass, I added the 143 kg of RCS propellant.

For the payload fairing I added 920 kg for the Orion Jettisoned Adaptors.

I increased the inclination to 28.45°.

I selected a non-restartable second stage and direct injection, which is the trajectory I simulated.

Now, you'd think all these changes would decrease payload, but the payload I got was 131.4 t, which is only 1.6 t or 1.2% less than my value. Perhaps you are using a different version program.
« Last Edit: 03/04/2014 08:38 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Rocket22

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Re: SLS Trajectory Simulations
« Reply #146 on: 08/16/2014 04:03 pm »
Steven,  you might be interested in a conceptual design and analysis computer program for rockets and their missions that I developed in retirement. It's called ZOOM and is free. It has a GUI and works with Windows XP, Windows 7, and Windows 8.1 operating systems. It can be used on tablet computers with touch-screens. It can be downloaded at:

http://trajectorysolution.com/zoom-7.zip

I first began developing rocket trajectory optimization programs in 1963 with Boeing in Huntsville, Alabama. We based our methods on the calculus of variations back then. As our simulations got more complicated we switched to parameter-optimization techniques. In 1973, at Northrop in Huntsville, I developed and used a method based on the Simplex algorithm (of Linear Programming fame) to define a quasi-optimum reentry trajectory for a Space Shuttle type vehicle. The objective was to minimize the aerodynamic heat load, and a limit was imposed on the aerodynamic heating rate. A modified version of that method is used by ZOOM.

In my view, ZOOM is a powerful tool for conceptual design and analysis. It's really sort of a miracle.... working much better than my experience would have led me to expect.

Best regards,

David F. Williams
Huntsville, Alabama, USA

Offline IslandPlaya

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Re: SLS Trajectory Simulations
« Reply #147 on: 08/16/2014 07:19 pm »
Steven,  you might be interested in a conceptual design and analysis computer program for rockets and their missions that I developed in retirement. It's called ZOOM and is free. It has a GUI and works with Windows XP, Windows 7, and Windows 8.1 operating systems. It can be used on tablet computers with touch-screens. It can be downloaded at:

http://trajectorysolution.com/zoom-7.zip

I first began developing rocket trajectory optimization programs in 1963 with Boeing in Huntsville, Alabama. We based our methods on the calculus of variations back then. As our simulations got more complicated we switched to parameter-optimization techniques. In 1973, at Northrop in Huntsville, I developed and used a method based on the Simplex algorithm (of Linear Programming fame) to define a quasi-optimum reentry trajectory for a Space Shuttle type vehicle. The objective was to minimize the aerodynamic heat load, and a limit was imposed on the aerodynamic heating rate. A modified version of that method is used by ZOOM.

In my view, ZOOM is a powerful tool for conceptual design and analysis. It's really sort of a miracle.... working much better than my experience would have led me to expect.

Best regards,

David F. Williams
Huntsville, Alabama, USA
Was looking forward to trying this David, but you seem to have missed including the .exe in your zip file...
Am I right?
Cheers mate.

Offline IslandPlaya

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Re: SLS Trajectory Simulations
« Reply #148 on: 08/16/2014 07:47 pm »
David kindly steered me to the 'ZOOM Program Directory' folder...
On my PC it didn't show up as the standard folder icon, but viola! The .exe is in there and it works.
Cheers

Offline IslandPlaya

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Re: SLS Trajectory Simulations
« Reply #149 on: 08/16/2014 08:00 pm »
Sorry, the party threads are leaking over...
By 'viola' I mean 'et voilà'

Offline IslandPlaya

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Re: SLS Trajectory Simulations
« Reply #150 on: 08/16/2014 08:24 pm »
Just had a quick play...
The UI leaves something to be desired, but that doesn't matter.
Awesome options and customisation. I trust David's experience and knowledge that the outputs are close to reality.
Looking forward to people using this to simulate their fave SpaceX rockets!

Offline Steven Pietrobon

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Re: SLS Trajectory Simulations
« Reply #151 on: 08/18/2014 07:44 am »
Thanks very much David. I look forward to trying your software in order to verify my simulations.

For the last few weekends, I have been updating my software to reflect the latest information on the RSRMV boosters, core, RS-25E engines and J-2X engines. There are some substantial payload increases due to the lighter core, higher thrust RS-25E and the long nozzle version of the J-2X. Below is a summary of the results. Attached are pdf's giving the details. The payloads given below are for a 200 km circular orbit where the payload also consists of an Orion crew vehicle.

Name        Boosters   RS-25E   J-2X   Payload (t)
--------------------------------------------------
SLS1C4J1.1   RSRMV       4       1     113.6
SLS1C5J2.1   RSRMV       5       2     130.6
SLS1C6J2.1   RSRMV       6       2     137.0
SLS2C4J2.1   2xF-1B      4       2     139.7
SLS3C4J2.1   3xAJ1E6     4       2     142.9
SLS4C4J2.1   ATK AB      4       2     131.5


Of interest is that we can get 130 t payload (not IMLEO) using either Block I RSRMV boosters and a five engine core or with ATK Advanced Boosters (aka Dark Knights) with a Block I four engine core.
« Last Edit: 08/18/2014 07:45 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Rocket22

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Re: SLS Trajectory Simulations
« Reply #152 on: 08/18/2014 02:47 pm »
Your work is very interesting. It will be good to see how your ZOOM results compare to those you have obtained for the various configurations.

In checking out ZOOM, I experimented with various imagined configurations, knowing practically nothing about what was actually being contemplated by those with the resources to develop new launch vehicles. For example, I looked at attaching five SSME's to the base of the Space Shuttle external tank, with full LOX/LH2 propellant load, and attaching a couple of SRB's with the approximate performance of the Space Shuttle SRB's and a second LOX/LH2 stage using one J2-S engine   ZOOM indicated that this vehicle could deliver a little over 140 t (gross) to a 220 km circular orbit, with a liftoff mass less than 2388 t. The SSME's were throttled down in 5% steps to keep axial acceleration from exceeding 3 g's. When the SSME's thrust had been reduced to 60% of design value, the SRB's burned out and were ejected. The SSME's then throttled back up to about 90% and maintained that level to the staging point. The optimization was constrained so that maximum dynamic pressure during ascent did not exceed 37.6 kN/m^2. Of the total mission ideal delta-V of 9220 m/s, the J2-S stage delivered 2982 m/s, the external-tank/SSME first stage delivered 4414 m/s, and the SRB's delivered 1824 m/s. The flight time was about 816 sec, and orbit injection occurred about 3333 km downrange. The ascent steering was constrained so that the rocket's normal acceleration did not exceed 0.01 g.

I welcome any feedback you may offer concerning ZOOM. One user is planning to provide a model for calculation of inert mass that is more substantive than the present one, where the user simply specifies a propellant mass fraction. I have to try and achieve a good balance between the program's usability and its complexity.

I appreciate your interest and look forward to hearing from you again.


Offline Oli

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Re: SLS Trajectory Simulations
« Reply #153 on: 03/14/2015 04:14 pm »
Thanks very much David. I look forward to trying your software in order to verify my simulations.

For the last few weekends, I have been updating my software to reflect the latest information on the RSRMV boosters, core, RS-25E engines and J-2X engines. There are some substantial payload increases due to the lighter core, higher thrust RS-25E and the long nozzle version of the J-2X. Below is a summary of the results. Attached are pdf's giving the details. The payloads given below are for a 200 km circular orbit where the payload also consists of an Orion crew vehicle.

Name        Boosters   RS-25E   J-2X   Payload (t)
--------------------------------------------------
SLS1C4J1.1   RSRMV       4       1     113.6
SLS1C5J2.1   RSRMV       5       2     130.6
SLS1C6J2.1   RSRMV       6       2     137.0
SLS2C4J2.1   2xF-1B      4       2     139.7
SLS3C4J2.1   3xAJ1E6     4       2     142.9
SLS4C4J2.1   ATK AB      4       2     131.5


Of interest is that we can get 130 t payload (not IMLEO) using either Block I RSRMV boosters and a five engine core or with ATK Advanced Boosters (aka Dark Knights) with a Block I four engine core.

I put those numbers (SLS4C4J2.1) into Schilling's rocket calculator which gives me approx. 127t to LEO. Funny thing is, if I add 2 additional ATK ABs to the rocket it increases the payload by 45t to 172t.

It that realistic?
« Last Edit: 03/14/2015 04:37 pm by Oli »

Offline TomH

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Re: SLS Trajectory Simulations
« Reply #154 on: 03/14/2015 09:58 pm »
I put those numbers (SLS4C4J2.1) into Schilling's rocket calculator which gives me approx. 127t to LEO. Funny thing is, if I add 2 additional ATK ABs to the rocket it increases the payload by 45t to 172t.

It that realistic?

If that were affordable, you may as well air start the core after booster burn out and let the core be a second stage. Making RS-25 air startable would be quite expensive though.

Regardless of that, adding more boosters is problematic and costly. The upper thrust beam would have to be redesigned. The crawleway can't support that much weight, so the thing would sink and collapse on its way to the pad. The ML and flame trenches would require complete redesign and modification. The acoustic and harmonic loads might destroy the core. The acoustic load may be too high and illegal as it might blow out windows all over the central Florida coast. Pretty full of problems, really.
« Last Edit: 03/14/2015 10:08 pm by TomH »

Offline TomH

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Re: SLS Trajectory Simulations
« Reply #155 on: 03/14/2015 10:45 pm »
Assuming BFR doesn't provide the impetus to cancel SLS (I think it will), the final evolved iteration the rocket would have is 2 Dark Knight advanced composite boosters, 4xRS-25 core, and upgraded EUS with MB-60 (MARC-60) engines (although EUS will primarily be EDS and engines will contribute only a circ. burn to LEO). Steven (or anyone), have you run calculations on this permutation?

Offline Steven Pietrobon

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Re: SLS Trajectory Simulations
« Reply #156 on: 03/17/2015 03:25 am »
Tom, the closest I have is Dark Knights, 4xRS-25E core and 2xJ-2X upper stage. I only got 124.8 t to LEO (9,787 m/s delta-V). The limiting factor here is the core thrust. It needs to be greater in order to reduce gravity losses. Going to five engines on the core reduces delta-V to 9,320 m/s with payload increasing to 144.1 t.
« Last Edit: 03/17/2015 03:27 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline TomH

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Re: SLS Trajectory Simulations
« Reply #157 on: 03/17/2015 03:20 pm »
Tom, the closest I have is Dark Knights, 4xRS-25E core and 2xJ-2X upper stage. I only got 124.8 t to LEO (9,787 m/s delta-V). The limiting factor here is the core thrust. It needs to be greater in order to reduce gravity losses. Going to five engines on the core reduces delta-V to 9,320 m/s with payload increasing to 144.1 t.

Steven, is that running the RS-25s at high throttle and then using a considerable amount of the EUS impulse to attain LEO, or are you burning the core to disposal orbit and using the EUS only for a circ burn, then including its remaining mass as an IMLEO amount?  The reason I am asking is if the latter acenario is the case, an RL-10 powered EUS should be little different than the J-2X version. If you're using the EUS impulse mainly to reach LEO, then the RL-10s take greater gravity losses.

With the parameters NASA has set for Block IIB (Dark Knight boosters), I am wondering what the final numbers will be.

Offline Steven Pietrobon

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Re: SLS Trajectory Simulations
« Reply #158 on: 03/18/2015 03:56 am »
The J-2X upper stage is performing a substantial part of the orbital insertion. With four engined core it is 3255 m/s and with five engines it is 3144 m/s. I am assuming a separate stage performs TLI. Having the core do an additional 3 km/s will substantially reduce payload due to the heavy dry mass of the core of over 100 t. I used a core dry mass of 115.6 t with four engines.
« Last Edit: 03/18/2015 03:57 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

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