Author Topic: SLS General Discussion Thread 3  (Read 310792 times)

Offline Archibald

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Re: SLS General Discussion Thread 3
« Reply #580 on: 03/21/2019 05:58 am »
Quote
SLS first launch was supposed to be no later than December 31, 2016, as specified in the NASA Authorization Act of 2010.
 

I never realized before they had fixed a date to fly that beast...
And I'm pretty shocked by that said date. December 2016 WTH ? Quite a long time ago...!!!
Unbelievable how the politics behind that 2010 SLS deal were insane and dishonest at the same time. Sickening, really sickening.
« Last Edit: 03/21/2019 06:01 am by Archibald »
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Offline woods170

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Re: SLS General Discussion Thread 3
« Reply #581 on: 03/21/2019 08:10 am »
Quote
SLS first launch was supposed to be no later than December 31, 2016, as specified in the NASA Authorization Act of 2010.
 

I never realized before they had fixed a date to fly that beast...
And I'm pretty shocked by that said date. December 2016 WTH ? Quite a long time ago...!!!
Unbelievable how the politics behind that 2010 SLS deal were insane and dishonest at the same time. Sickening, really sickening.

When the date of December 2016 was put into law it took NASA just a few months to announce that they wouldn't be able to make that date. December 2017 was the earliest NET they could give.

Offline Archibald

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Re: SLS General Discussion Thread 3
« Reply #582 on: 03/21/2019 09:16 am »
Quote
SLS first launch was supposed to be no later than December 31, 2016, as specified in the NASA Authorization Act of 2010.
 

I never realized before they had fixed a date to fly that beast...
And I'm pretty shocked by that said date. December 2016 WTH ? Quite a long time ago...!!!
Unbelievable how the politics behind that 2010 SLS deal were insane and dishonest at the same time. Sickening, really sickening.

When the date of December 2016 was put into law it took NASA just a few months to announce that they wouldn't be able to make that date. December 2017 was the earliest NET they could give.

note that I blamed especially politics and not NASA. And you confirm even NASA felt the politics were insane or absurd or both.
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Offline woods170

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Re: SLS General Discussion Thread 3
« Reply #583 on: 03/21/2019 11:21 am »
Quote
SLS first launch was supposed to be no later than December 31, 2016, as specified in the NASA Authorization Act of 2010.
 

I never realized before they had fixed a date to fly that beast...
And I'm pretty shocked by that said date. December 2016 WTH ? Quite a long time ago...!!!
Unbelievable how the politics behind that 2010 SLS deal were insane and dishonest at the same time. Sickening, really sickening.

When the date of December 2016 was put into law it took NASA just a few months to announce that they wouldn't be able to make that date. December 2017 was the earliest NET they could give.

note that I blamed especially politics and not NASA. And you confirm even NASA felt the politics were insane or absurd or both.

Correct. NASA was given an assignment by US Congress and figured out pretty quickly that within the available budget there was a snowball's chance in hell that SLS would launch in December 2016.
With regards to the politics at play: there is a reason why SLS is sometimes mockingly called the 'Senate Launch System'.

Offline Rondaz

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Re: SLS General Discussion Thread 3
« Reply #584 on: 03/25/2019 06:44 pm »
Every indication I've gotten back from sources in Houston and DC is that the commercial Orion plan will be a "no-go." Not sure what technical reason will be given, but politically it is just too destructive to show Orion can be sent to the Moon by private rockets.

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Online darkenfast

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Re: SLS General Discussion Thread 3
« Reply #585 on: 03/25/2019 11:28 pm »
The commercial proposal broke the number one commandment: "Thou shalt not get between the pigs and their trough."
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Offline Lars-J

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Re: SLS General Discussion Thread 3
« Reply #586 on: 03/25/2019 11:49 pm »
Sure, the commercial EM-1 is not going to happen, but anyone who believes that SLS is safe and unchanging "because the senate" is in for a rude surprise.

Congress will likely roll back some proposed things, but not all the way. Obama cancelled CxP, but only SLS+Orion survived to be resurrected.

If the administration wants to cancel SLS and/or Orion, one of them will likely be cancelled and/or scaled back. Whatever survives will be in a diminished state. Many SLS backers remain in Congress, but many have also left office.

Online redliox

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Re: SLS General Discussion Thread 3
« Reply #587 on: 03/26/2019 12:29 am »
Sure, the commercial EM-1 is not going to happen, but anyone who believes that SLS is safe and unchanging "because the senate" is in for a rude surprise.

----

If the administration wants to cancel SLS and/or Orion, one of them will likely be cancelled and/or scaled back. Whatever survives will be in a diminished state. Many SLS backers remain in Congress, but many have also left office.

Proves how politics and science mix like water and oil.

More specifically, the key point is that senators (and representatives) change in and out frequently, so the collective whim with NASA will change...alot...at least over the course of decades.  The 1960s were dominated by the race against the USSR, the '70s were by the recession, the '80s by showboating via the shuttle (until, of course, Challenger), and the '90s/2000s saw a revival in science via the Discovery and Mars programs.  The current batch of Congressmen will likely hold onto SLS as long as possible, but in the next 6 to 10 years the new wave (especially [forgive if touching on current volatile politics] if a heavier bias against Trump prevails) will issue new orders in light of how commercial rockets preform versus SLS (moreso if SLS still hasn't launched before 2020).

My current thoughts for what the future Congress' orders for NASA will be:
1) There will be fewer flights of SLS (say maybe 5, dictated by funds and the number of shuttle parts available).
2) No collusion collaborating with Russia
3) More opportunities for the likes of Blue Origins and SpaceX
4) No flight for Europa Clipper, although perhaps either another Outer Planet or Astronomy mission flies via SLS

I do have hopes for the SLS, but I will be disappointed if they don't at least get to the Block IB stage; I already figured Block 2 would be impossible but the EUS' lift is vital; Block I was always a joke flight.
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Offline Zed_Noir

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Re: SLS General Discussion Thread 3
« Reply #588 on: 03/26/2019 02:06 am »
....
I do have hopes for the SLS, but I will be disappointed if they don't at least get to the Block IB stage; I already figured Block 2 would be impossible but the EUS' lift is vital; Block I was always a joke flight.

You might be right about a few SLS flights. Recall there is enough shuttle spare parts for 4 SLS flights.

However the EUS stage appears to be on the budgetary chopping block and additional iCPS being ordered. It appears the only version of the SLS being introduces into service is the Block 1 as a cis-Lunar launcher for the Orion stack. So you will probably be disappointed with the SLS.

However there are alternative heavy lift on the horizon.

edit - typo
« Last Edit: 03/26/2019 11:18 pm by Zed_Noir »

Offline Coastal Ron

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Re: SLS General Discussion Thread 3
« Reply #589 on: 03/26/2019 03:09 am »
Many SLS backers remain in Congress, but many have also left office.

I don't think there have ever been many SLS backers in Congress, just that there haven't been many anti-SLS people in Congress - it's budget is small enough to be put in the category of "there are bigger fish to fight over".

But I think people keep forgetting that it's not how much funding the SLS gets, it's how much funding PAYLOADS and MISSIONS for the SLS gets. Because what good is a rocket if there is no use for it?

And so far multiple Congress (i.e. 112th, 113th, 114th and 115th) have not been enthusiastic about funding payloads and programs for the SLS to support, and that is really the indication of the future of the SLS. We'll see what the 116th Congress funds, and that will indicate how many SLS backers there really are in Congress.
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Offline clongton

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Re: SLS General Discussion Thread 3
« Reply #590 on: 03/26/2019 11:46 am »
4) No flight for Europa Clipper, although perhaps either another Outer Planet or Astronomy mission flies via SLS

Europa Clipper will fly, but imo not on the SLS. While we wait and wait and wait and wait and wait (you get the picture) for SLS to finally fly, the Europa Clipper people are getting more and more frustrated with all the dicking around with their spacecraft just to have something fly on SLS to justify its existence. They want their spacecraft to fly before the instruments become outdated, are ancient and yesterday's technology. Expect a major push to decouple Clipper from SLS.

As an alternative to SLS the Falcon Heavy expendable can fly Europa Clipper. Delta-v to Jupiter is 6.3 km/s. Falcon Heavy expendable can send 7.7 t directly to Jupiter. Launch mass of Europa Clipper is 6.0 t. That existing capability is not lost on the science community as their frustration levels continue to rise as they keep waiting and waiting and waiting and waiting.
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Online ugordan

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Re: SLS General Discussion Thread 3
« Reply #591 on: 03/26/2019 12:00 pm »
Falcon Heavy expendable can send 7.7 t directly to Jupiter.

That number does not hold water.

Online envy887

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Re: SLS General Discussion Thread 3
« Reply #592 on: 03/26/2019 12:47 pm »
Falcon Heavy expendable can send 7.7 t directly to Jupiter.

That number does not hold water.

Agree. Even with a STAR-48, the best case is 5.5 t to a C3 of 80 km2/s2, assuming SpaceX's advertised 26.7 t to GTO-1800 is accurate and the upper stage burnout mass is also 5.5 t.

Offline Lobo

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Re: SLS General Discussion Thread 3
« Reply #593 on: 03/26/2019 02:08 pm »
Falcon Heavy expendable can send 7.7 t directly to Jupiter.

That number does not hold water.

Agree. Even with a STAR-48, the best case is 5.5 t to a C3 of 80 km2/s2, assuming SpaceX's advertised 26.7 t to GTO-1800 is accurate and the upper stage burnout mass is also 5.5 t.

That number is actually from Steven Pietrobon.  I'll double check it with him.

Online ugordan

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Re: SLS General Discussion Thread 3
« Reply #594 on: 03/26/2019 06:57 pm »
Falcon Heavy expendable can send 7.7 t directly to Jupiter.

That number does not hold water.

Agree. Even with a STAR-48, the best case is 5.5 t to a C3 of 80 km2/s2, assuming SpaceX's advertised 26.7 t to GTO-1800 is accurate and the upper stage burnout mass is also 5.5 t.

This is straying offtopic, but I was wondering why only a direct trajectory via a kickstage was apparently in the trade space and not a Juno-like trajectory without a kick stage.

Well, Juno was launched with a C3 of just over 30 km^2/s^2 and it had to perform a deep space maneuver of over 700 m/s to properly set up the Earth flyby. Extrapolating this to Clipper, it would need over 1,5 tonnes of extra propellant (with an 316 s Isp engine) over the 6 tonne launch mass baselined for the direct-to-Jupiter injection. This brings it quite close to the stated NASA LSP throw mass of FH of around 8 tonnes to that C3, and that is while incurring an *extra* 2 years of cruise time. Given launch period variations and other factors (impacting both injection C3 and DSM delta-V), I can understand that the tradeoff and delta-V margin is not as good as I originally thought for a Juno-like trajectory.

However, that margin still appears to be healthier than what Juno had with Atlas V 551 so go figure...

Online oldAtlas_Eguy

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Re: SLS General Discussion Thread 3
« Reply #595 on: 03/27/2019 04:15 am »
Well it is now launch it already or get out of the way. Unfortunately congress will resist letting SLS get out of the way. The pressure is on and not just by the administration. With commercial advancing quickly it provides additional incentives.

Offline Steven Pietrobon

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Re: SLS General Discussion Thread 3
« Reply #596 on: 03/27/2019 05:32 am »
Agree. Even with a STAR-48, the best case is 5.5 t to a C3 of 80 km2/s2, assuming SpaceX's advertised 26.7 t to GTO-1800 is accurate and the upper stage burnout mass is also 5.5 t.

Here are my sums. Please show yours!

That 5.5 t value for the FUS burn out mass is way too high. I was using 4.0 t, as given in

http://spaceflight101.com/spacerockets/falcon-heavy/

The only dry mass value for FUS that has leaked out was for SpX-6 in April 2015 flying on v1.1. That value was 3.73 t. FUS v1.2 was stretched a little, so a value of 4.0 t is entirely reasonable.

We are also not using a STAR-48. We are assuming direct injection by FUS. Note that from a GTO orbit, the extra delta-V required to get to Jupiter is (assuming 7.8 km/s LEO orbit speed and 2.44 km/s GTO speed) is sqrt(2*7.8*7.8+80)-7.8-2.44 = 4.0 km/s.

I use a linear model of the delta-v and the performance of the stage to predict its performance with lighter payloads. We first determine the delta-V for FUS for LEO given a 63.8 t payload. This is vi = ve*ln(1+mp/(ms+mc0)) = 3241.85 m/s, where

ve = 3412.7 m/s
mp = 107.5 t
ms = 4.0 t
mc0 = 63.8 t

We then determine scale factor vm, using the additional delta-V (dv1) from LEO for a payload mass mc1. Our linear model for the actual delta-V of the stage (dv) is

dv = vm*dv1 + vi

The stage delta-V is

dv = ve*ln(1+mp/(ms+mc1))

gives

vm = (ve*ln(1+mp/(ms+mc1))-vi)/dv1

Using the three payloads masses beyond LEO, we have

Destination  dv1 (m/s)  mc1 (t)  vm
GTO          2440       26.7     0.775554
Mars         3600       16.8     0.824244
Pluto        8360        3.5     0.726665


We can see that the three values of vm are fairly close to each other (within ±6% of the average), indicating that this is a pretty good model. We are using the delta-V values obtained from this chart.

https://forum.kerbalspaceprogram.com/index.php?/topic/131682-is-there-a-delta-v-chart-for-real-solar-system-mod/

SpaceX could have used different values, which may explain some of the differences. In any case, let us use the average value of vm, which is 0.775488 (pretty close to the GTO value). The delta-V to Jupiter is dv = 6300 m/s. This then allows us to calculate the payload mass as

mc = mp/(exp((vm*dv+vi)/ve)-1)-ms = 6.95 t.

This answer is different to my previous value, since I updated some of the values in my model. In any case, this is still more than what is required for FH-E to send Europa Clipper to Jupiter.

If we use a dry mass of 5.5 t and obtain a new vi = 3196.2 m/s and vm = 0.729175, the model gives a payload mass of 6.71 t, which is still more than enough. I'm not exactly sure why the model is not so sensitive to dry mass. Mathematically, it is due to both vi and vm decreasing in value, which reduces the value of dv, thus compensating for the increase value of ms.

You can download the software for this model from the link below.

http://www.sworld.com.au/steven/space/fh.zip
« Last Edit: 03/27/2019 05:32 am by Steven Pietrobon »
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Offline ncb1397

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Re: SLS General Discussion Thread 3
« Reply #597 on: 03/27/2019 07:29 am »
C3 of 80 to Jupiter is pretty optimistic.

Ames' trajectory browser lists a few trajectories in the 2020s direct to Jupiter with <80 C3. In a search, they all launch on December 31st 2028. Next highest is July 11th 2023 with a C3 of 80.4. If you want to pick your year - assume 90.

https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Jupiter&mission_class=oneway&mission_type=rendezvous&LD1=2020&LD2=2030&maxDT=3&DTunit=yrs&maxDV=8&min=DV&wdw_width=-1&submit=Search#a_load_results

You also have to account for that these are optimized trajectories with exact dates. You have to design for like - a 1 month window. For instance, the December 31st 2018 trajectories change from a minimum of C3=76.6
to a minimum of C3=83.1 2 weeks earlier on December 15th.

For what it is worth, the LSP performance query lists performance for Expendable Falcon Heavy as 1425 kg for C3=90.

Anyways, JPL (specifically, the Europa Clipper boss) should have already settled this debate:

Quote
The breakthrough referenced by Goldstein involved the addition of a Star 48 "kick stage" to the Falcon Heavy rocket, which would provide an extra boost of energy after the rocket's upper stage had fired. With this solid rocket motor kick stage, Goldstein said Clipper would need just a single Earth gravity assist and would not have to go into the inner Solar System for a Venus flyby.
https://arstechnica.com/science/2018/12/will-the-europa-missions-be-iced-after-congressmans-defeat-not-right-now/3/

They may also be accounting for engine out on the booster. This has happened once so far in ~70 flights. With a Falcon Heavy, the odds triple. Europa Clipper might have looked at this and didn't like those 5% odds.

Destination  dv1 (m/s)  mc1 (t)  vm
GTO          2440       26.7     0.775554
Mars         3600       16.8     0.824244
Pluto        8360        3.5     0.726665

Not sure how to reconcile these numbers with LSP numbers. These may be theoretical numbers without a fairing(like dragon) while LSP specifically lists the 5.2 meter fairing.
« Last Edit: 03/27/2019 09:31 am by ncb1397 »

Offline woods170

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Re: SLS General Discussion Thread 3
« Reply #598 on: 03/27/2019 09:56 am »
Quick question: why is Falcon Heavy being discussed in a thread that is about SLS?

Offline Lobo

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Re: SLS General Discussion Thread 3
« Reply #599 on: 03/27/2019 04:40 pm »
Quick question: why is Falcon Heavy being discussed in a thread that is about SLS?

Because there's a reasonable chance FH could take a flagship mission from SLS in Europa Clipper...if it has the required performance.

Ditto for the possibility of Orion being moved to it for EM-1.

Either or both of those would have an impact on SLS in various ways, hence being discussed on the SLS Thread.
« Last Edit: 03/27/2019 04:41 pm by Lobo »

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