SLS engines questions...

[Hcube]

Just wondering about a few things :

(can't say that i did an exhaustive search, but a 30s look up told me nothing about this)

What engines will be on the first stage of the SLS part from the 2SRBs ? I heard about SSMEs, but how many of them ? will they be modified ? will they have enough thrust to lift this monster ?

What engines will run on the second stage if the SLS ? I read somewhere that the future Ariane 6's Vinci engine built by Snecma was considered to be used, but it has ridiculously low thrust (although amazing Isp). Is this still ongoing ? if so, will there be a cluster of those ? If not, what engines ?

(PS ; when is the first SLS flight planned ?) (feel free to correct any english mistakes i made, that would help me improve in english)

Edited May 29, 2015 by Hcube

[Reddragon]

The SLS first stage will use 4 SSME (RS-25) engines. I don't know about the second stage.

Here's the aerodynamic test model:

[_Augustus_]

4 SSME's are plenty powerful to lift the SLS.

First off, the first flight is planned for 2018, it is a Block I. There were plans for a 3-engine Block 0 to be launched earlier for demo and ISS docking missions, but there are no plans currently to use one, and if they want to do ISS missions with Orion a 4-SRB Ariane 5 or 6 or a Delta IV Heavy can bring it there for a lower cost.

The Block I uses the ICPS as an upper stage. It has no engine name.

Blocks IB-II use the Exploration Upper stage, powered by 4 RL-10 engines.

There are also plans for a Block III, which uses a J2-X upper stage engine, 5 SSME's instead of 4, and giant F1-B liquid fuel boosters.

About the boosters: Blocks I and IB use 5-segment Shuttle SRB's, and the proposed Block IA (Block I with advanced SRB's but still ICPS instead of EUS) and would use advanced SRB's. The Block II will also use the same advanced SRBs.

[Kryten]

What engines will be on the first stage of the SLS part from the 2SRBs ? I heard about SSMEs, but how many of them ? will they be modified ? will they have enough thrust to lift this monster ?

Four Aerojet Rocketdye RS-25s. The first flights will use surplus RS-25Ds (AKA SSMEs), and later flights a cheaper, simplified version called RS-25E. Further on the current steel-cased SRBs are also planned to be replaced; by a composite-cased design, known informally as 'dark knight'.

What engines will run on the second stage if the SLS ? I read somewhere that the future Ariane 6's Vinci engine was considered to be used, but it has ridiculously low thrust (although amazing Isp). Is this still ongoing ? if so, will there be a cluster of those ? If not, what engines ?

Initially it's planned to use an Interim Cryogenic Upper Stage; a modified Delta IV upper stage, using the RL-10B engine (also from AR). Later flights will use the larger Exploration Upper Stage, using four RL-10Cs.

(PS ; when is the first SLS flight planned ?)

Current official schedule is 'no later than November 2018', working date is July 2018.

Edited May 30, 2015 by Kryten

[cryogen]

What engines will be on the first stage of the SLS part from the 2SRBs ? I heard about SSMEs, but how many of them ? will they be modified ? will they have enough thrust to lift this monster ?

Actually, they won't! The first stage (core, excluding boosters) will have 7,440 kN of sea-level thrust (4x RS-25), and a gross mass of 979 tonnes, for a TWR of about 0.78. The main engines wouldn't be able to the lift the first stage above the ground.

https://en.wikipedia.org/wiki/Space_Launch_System

(sidebar)

The same was true of the Shuttle. The main engines didn't have enough thrust to lift the external tank, which was their fuel source.

The Block I uses the ICPS as an upper stage. It has no engine name.

I believe it's the same RL-10B2 as the DCSS -- here's a source:

For the ICPS, The Boeing Co. will modify its existing Delta Cryogenic Second Stage, used on United Launch Alliance’s Delta IV family of launch vehicles. It will be powered by an Aerojet Rocketdyne RL-10B2 engine -- also currently used on the Delta Cryogenic Second Stage.

"Boeing's Delta Cryogenic Second Stage will need relatively minor modifications to be fully compliant with SLS requirements, which will keep us on schedule for the first two flights," said Chris Calfee, ICPS project manager at NASA's Marshall Space Flight Center in Huntsville, Alabama. Marshall manages the SLS Program for the agency.

https://www.nasa.gov/sls/interim_cryogenic_propulsion_stage_141030.html

Edited May 30, 2015 by cryogen

[Kryten]

There are also plans for a Block III, which uses a J2-X upper stage engine, 5 SSME's instead of 4, and giant F1-B liquid fuel boosters.

SLS has no provision for installation of a fifth core engine, J-2X is no longer under development, and NASA has no intention to plumb the pad for liquid boosters (hence the cancellation of the advanced booster competition). Whatever you got this from, it's extremely outdated.

[Bill Phil]

SLS has no provision for installation of a fifth core engine, J-2X is no longer under development, and NASA has no intention to plumb the pad for liquid boosters (hence the cancellation of the advanced booster competition). Whatever you got this from, it's extremely outdated.

There are, however, problems with using only four. The LOX pressure is too high...

At least, according to someone directly working on the SLS.

[Hcube]

Thank you for you answers.

@_Augustus_ : about Orion docking missions : I don't think you can stick an Orion on top of an ariane 5 or 6. Anyway the ariane 5 is not rated for human flight, its installations in Guyana dont allow crewed vehicles launches... And you can't strap 4boosters to an ariane 5...

I think Delta 4 will do

[A1Ch1]

There are, however, problems with using only four. The LOX pressure is too high...

At least, according to someone directly working on the SLS.

The increased pressure isn't from using four vs five engines. The reason is the core is taller than the ext tank and stack will accelerate at a max of 3.3 g vs the shuttle's 3 g. This results in a LOX head pressure of ~1.8 MPa vs the shuttle's typical 1.2 MPa. Part of the engine testing program is to certify for the increased pressure.

Edited June 2, 2015 by A1Ch1

[Tankbuster32]

The Delta 4 isn't man-rated either IIRC.

[Hcube]

The Delta 4 isn't man-rated either IIRC.

Isn't it ? but,doesn't that mean that Orion will only be launchable atop the SLS ? Wouldn't that be overkill for small-scale missions ?

EDIT : very quick research brought this up :

The United Launch Alliance (ULA) published a paper submitted to AIAA detailing the modifications to its Delta IV and Atlas V launch vehicles that would be needed to conform to NASA Standard 8705.2B. ULA has since been awarded $6.7 million under NASA's Commercial Crew Development (CCDev) program for development of an Emergency Detection System, one of the final pieces that would be needed to make these launchers suitable for human spaceflight.

(Mind you this is from wikipedia, so it is entirely possible that a big part of it may be wrooooong)

Edited June 2, 2015 by Hcube

[Kryten]

Isn't it ? but,doesn't that mean that Orion will only be launchable atop the SLS ? Wouldn't that be overkill for small-scale missions ?

Orion is a specialised deep-space vehicle, it's not meant to do any 'small-scale missions'. That's the job of the CCDEV vehicles, CST-100 and Dragon 2.

[Hcube]

Orion is a specialised deep-space vehicle, it's not meant to do any 'small-scale missions'. That's the job of the CCDEV vehicles, CST-100 and Dragon 2.

Oh okay i see. I thought that Orion was also planned to do a few preliminary LEO missions.

How is CST-100 supposed to be launched then ?

(we are drifting away from the OP subject, but as long as it's interesting let's keep it going)

[Kryten]

How is CST-100 supposed to be launched then ?

Atlas V, specifically the 422 variant (2 boosters, double-engined Centaur).

Oh okay i see. I thought that Orion was also planned to do a few preliminary LEO missions.

Some Orion flights to the ISS were planned back when it was still part of the constellation program, as a backup in case the CCDEV vehicles weren't ready in time. That was cancelled because Orion would've been far more expensive, and it being ready before a CCDEV vehicle was looking very implausible.

Edited June 2, 2015 by Kryten