Author Topic: SLS Concept of Operations (Con Ops) Articles (Read 33667 times)

Chris Bergin · « **on:** 11/30/2011 08:50 pm »

Paul Howard · « **Reply #1 on:** 11/30/2011 10:53 pm »

Thanks! This is very much in the area of my interest. Looking forward to the next ones!

On the latest. One week of flow at the pad, that's interesting!

Chris Bergin · « **Reply #2 on:** 11/30/2011 11:32 pm »

Thanks Paul. We'll have a good run of SLS articles - on various elements, mainly MISSIONS, through December

Jason Sole · « **Reply #3 on:** 12/01/2011 12:54 am »

Great to see how the baseline work is now moving forward.

Longhorn John · « **Reply #4 on:** 12/01/2011 02:27 pm »

Two really interesting articles. Maybe a thread title change to get more people to read it as "Concept of Operations" may appear to be a bit dull, when it really is anything but dull!?

Chris Bergin · « **Reply #5 on:** 12/01/2011 02:47 pm »

Quote from: Longhorn John on 12/01/2011 02:27 pm

Two really interesting articles. Maybe a thread title change to get more people to read it as "Concept of Operations" may appear to be a bit dull, when it really is anything but dull!?

I think the title is cool and anyone who is looking for "OMG, SLS costs a lot of money and Senator Nelson personally drew up the presentations and forced NASA to use them" thread titles should head down the corridor, take a left, open the door, walk out and close the door behind them

We're about the hardware here.

mjp25 · « **Reply #6 on:** 12/01/2011 03:02 pm »

It might be too soon to ask this, but I'd be interested in knowing the timing of RS-25 start up and SRB ignition. Given that SLS will not have the twang issue that STS had, will we see a shorter time between the two events? Or will the extra time still be used to verify RS-25 health before launch commit? Thanks.

Harold KSC · « **Reply #7 on:** 12/01/2011 03:18 pm »

Excellent articles. This is really important to cover as the refinements will be based from this.

Quote from: mjp25 on 12/01/2011 03:02 pm

It might be too soon to ask this, but I'd be interested in knowing the timing of RS-25 start up and SRB ignition. Given that SLS will not have the twang issue that STS had, will we see a shorter time between the two events? Or will the extra time still be used to verify RS-25 health before launch commit? Thanks.

Very good question. I will ask.

Namechange User · « **Reply #8 on:** 12/01/2011 07:16 pm »

Quote from: Harold KSC on 12/01/2011 03:18 pm

Excellent articles. This is really important to cover as the refinements will be based from this.

Quote from: mjp25 on 12/01/2011 03:02 pm
It might be too soon to ask this, but I'd be interested in knowing the timing of RS-25 start up and SRB ignition. Given that SLS will not have the twang issue that STS had, will we see a shorter time between the two events? Or will the extra time still be used to verify RS-25 health before launch commit? Thanks.

Very good question. I will ask.

I would expect the core engines to start prior to T-0, just as they did on Shuttle. The reason is not due to any twang effect but for them to come up to speed and GLS and engine health-monitoring to very everything within normal parameters. Solids just go, and once they are on, they are on. Likely this would be initiated right at T-0.

If SLS eventually goes to liquid boosters, then that could change and engine start for all is at T-0, followed by a checkout and release of the clamps sometime after T-0.

Chris Bergin · « **Reply #9 on:** 12/01/2011 08:01 pm »

This interests me too.

Best ever super slow mo video of SSME ignition...
http://forum.nasaspaceflight.com/index.php?topic=15312.0

Engines ramp up, need to say "we're at 104 percent", need to gimbal to start position, then they are ready to go.

I assume the three AHMS' talk to the GPCs to confirm the above to the GLS. But I too was under the misconception 6.6 seconds is required to allow for the stack to twang back level. No twang on SLS, but still 6.6 seconds for the SSMEs to confirm readiness on the GLS?

Jim · « **Reply #10 on:** 12/01/2011 08:04 pm »

SSME's are ready at T-3.x (don't remember the exact number). The remaining time was for twang. So, there should be a change in the countdown for SLS.

Shuttle Man · « **Reply #11 on:** 12/01/2011 08:11 pm »

This is a good question. They'll be up to 104 by 3.5 seconds or so, but that's not the whole deal. They need a "period" of monitoring to ensure they are holding at good levels and no redlines that could trip the GLS, so I wouldn't be surprised if they held at up to 5-6 seconds on SLS. As OV says, it's not all about the twang.

AnalogMan · « **Reply #12 on:** 12/01/2011 08:48 pm »

Timing for the shuttle start is shown in the attached graphic. This requires the SSMEs to be at >90% of final chamber pressure within 4 seconds of starting, else a pad shut-down is initiated.

From that decision point there are 2.5 seconds remaining until T-0 when the SRB fire command is issued. Not sure if this is solely to accommodate the twang, or whether other events need to be allowed for.

So potentially it might be possible that the SLS sequence could be shortened by a up to 2.5 seconds compared with shuttle.

psloss · « **Reply #13 on:** 12/01/2011 09:10 pm »

Will be just as interested in the terminal sequence before launch/liftoff commit for this LV, but another nit with Shuttle: the engines "only" throttled up to 100% on the pad and then went up to 104/104.5% shortly after liftoff.

Jim · « **Reply #14 on:** 12/01/2011 11:42 pm »

Quote from: Shuttle Man on 12/01/2011 08:11 pm

This is a good question. They'll be up to 104 by 3.5 seconds or so, but that's not the whole deal. They need a "period" of monitoring to ensure they are holding at good levels and no redlines that could trip the GLS, so I wouldn't be surprised if they held at up to 5-6 seconds on SLS. As OV says, it's not all about the twang.

It is because they were looking to do away with the twang delay, and try to launch when the SRB base moment was the same as at 6.6 sec. It was too early, at around 2.8 sec or so.

JohnFornaro · « **Reply #15 on:** 12/02/2011 07:31 pm »

What is the "twang" issue?

PahTo · « **Reply #16 on:** 12/02/2011 07:49 pm »

STS went through significant motion as the SSME's spooled up and were verified. If the SRBs had kicked in the moment the SSMEs were ready, the STS stack would have been effectively pointing N.

I'm with Jim--it'll be about 3.3 seconds for the engines to spool up before SRB ignition.
Nice attach Chris--tiny nit: the engines will gimble FROM the start position TO liftoff position once they're at full throat/startup transients clear. Along those lines, the accoustics of 5 RS-25s will be something to plan for at the base of the vehicle (see accoustic research at the back of the orbiters right up to the end of the program).

Quote from: JohnFornaro on 12/02/2011 07:31 pm

What is the "twang" issue?

kirghizstan · « **Reply #17 on:** 12/02/2011 07:51 pm »

Quote from: JohnFornaro on 12/02/2011 07:31 pm

What is the "twang" issue?

Here is a visual of the twang

Namechange User · « **Reply #18 on:** 12/02/2011 07:53 pm »

Quote from: JohnFornaro on 12/02/2011 07:31 pm

What is the "twang" issue?

There is no real issue with respect to SLS. "Twang" is the rocking back and forth of the shuttle stack at SSME ignition and the moment that is produced from the engines not being on centerline.

Engine start was timed for the engines to come to speed, check-out and make sure no parmaters were going to trip GLS as well as the period from the "twang", or rocking back and forth. T-0 hits when the the stack is pointing straight up from that period.

For SLS, there will no "twang" since the core engines are on centerline. However, you still will want to make sure they check-out and have no issues. SLS will also have solids (at least initially) and when they light, you go. So, it is logical to assume that the core engines will be started some number of seconds early to do that checkout. The command for booster ignition will be at T-0 and away you go.

Rocket Science · « **Reply #19 on:** 12/02/2011 09:23 pm »

I miss “the twang”…