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#226 2016-06-09 07:42:26

Tom Kalbfus
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Registered: 2006-08-16
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Re: The SLS: too expensive for exploration?

I think the rocket plume causes the air ahead of the rocket to expand out of the way, it is sort of like a standing explosion. the rocket also slows the rocket relative to the atmosphere so there is less frictional and compressive heating after the rocket burn.

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#227 2016-06-09 10:01:21

GW Johnson
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From: McGregor, Texas USA
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Re: The SLS: too expensive for exploration?

The first burn takes the stage upward and starts killing some of downrange velocity,  which is around 3 to 3.5 km/s (Mach 10-ish if there were any sensible air).  From there it accelerates downward under gravity toward the sensible air. This event takes place at orbital altitude (160+ km).

The second burn reduces vertical speed downward that was gained by falling under acceleration of gravity from orbital altitude,  or even more,  depending upon how high up the first burn took it.  At these speeds,  the sensible air interface is somewhere in the vicinity of 150,000 feet.  It's moving well above the nominal shown Mach 3 at the grid fin deployment point,  which would be somewhere around 100,000 feet.  They call it "hypersonic",  which for blunt objects is at least Mach 3-ish,  and for not-blunt objects (like this) is at or above Mach 5-ish. 

The third burn is the landing burn,  which takes them from supersonic to nothing at touchdown.  Don't forget,  it accelerates downward under gravity between burns.  But apparently they don't want it over Mach 3-ish with the grid fins deployed.  It has to be a whole lot slower than that to deploy the landing legs,  or the wind pressure will rip them right off. 

What I'm showing from compressible flow calculations is that the ideal gas model works well enough up to about 1.8 km/s speeds (about Mach 6 at 100,000 feet),  and above that,  the old reentry rule-of-thumb ("effective temperature in K is numerically equal to speed in m/s") gives you a better estimate of effective gas temperature.  That's because there is increasing dissociation above that speed.  The energy that would have raised total and recovery temperatures (and those two are not much different,  really) goes into ionization instead. 

At 100,000 feet,  the ambient static air temperature is 227 K.  At the 1.8 km/s / Mach 6 point,  total/recovery temperatures are about 1830 K.  Engine chamber gas temperatures are about 3000 K,  which is the stagnation temperature in the engine gas stream.  At 3 km/s (Mach 10) speeds,  the rule-of-thumb oncoming air effective temperature is also about 3000 K. 

The retropropulsion plume from the engine shocks down subsonic just behind the vehicle bow shock wave,  so it can turn downstream alongside the stage.  It reverts to pretty near its chamber temperature once subsonic like that,  and its recovery temperature still drives heat transfer rates,  even after it reaccelerates to supersonic alongside the stage tankage. 

Shocks are compression events,  not expansion events,  by the way. Post shock turns back streamwise are expansion events,  but these are localized.  That is what reaccelerates it supersonic alongside the tankage.

The oncoming air stream shocks down subsonic at the bow shock wave.  It goes to its effective temperature once subsonic,  and that temperature drives its heat transfer,  even after it reaccelerates supersonic alongside the tankage. 

So there are two very hot flows mixing alongside the tankage.  The gas is largely rocket plume gas right adjacent to the tankage.  Mixing is less than perfect,  to be sure.

I don't see any cooling effects or low speed effects here.  During the second burn,  they're trying to decelerate down to Mach 3,  so they can deploy the grid fins.  That means they are moving somewhere well above Mach 3 when they start that burn.  Mach 6?  Mach 10?  I don't know.  But very fast.  Both the local airstream and the plume gases are in the 3000 K class during this event,  all around the engines and tankage. 

I know these engines run slightly fuel rich at normal mixture,  but that doesn't explain the heavy sooting seen all over the bottom and sides of the stage.  As I said above,  I'd hazard the guess they're running a little kerosene through the inactive engines to keep their bells from overheating.  They look bad enough as it is,  with all the soot all over them,  but I don't see melt damage,  which should be evident if those bells were not protected in some way.  The meltpoint of carbon steel is only 1886 K,  by the way,  and stainless is a little lower than that,  actually. 

That kerosene flow would burn very inefficiently in the mixing slipstream,  which would put gobs of sooting all over everything exposed to that shocked flow,  but without adding much heat.  Spontaneous ignition of that kerosene is extremely like in the localized zones where recovery temperatures are high,  not so likely outside the boundary layers where things aren't so hot.  Vaporization absorbs some heat,  so there a localized cooling where that takes place. 

High speed aerodynamics is a complicated bitch,  ain't it?  So is maneuvering flight dynamics.  I did this crap for a living for over 20 years directly,  and over 40 years indirectly.  I might know just a little about the subject,  after all. 

GW

Last edited by GW Johnson (2016-06-09 18:29:28)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#228 2017-02-18 20:01:25

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 11,540

Re: The SLS: too expensive for exploration?

We have heard the recent wishes to change the EM-1 and EM-2 mission timelines to being a crewed mission1 and an actual landing on 2 which on paper would save about 15 billion out of the Nasa budgets but is it realistic.

Do this change the view point that sls is to expensive by just changing the time line?
I would say no as the price really has not changed but only the goal posts.....

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#229 2017-03-06 21:01:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 11,540

Re: The SLS: too expensive for exploration?

https://www.nasa.gov/sites/default/file … s_mr_0.jpg

The propulsion system that will give the Orion spacecraft the in-space push needed to travel thousands of miles beyond the moon and back has completed major assembly at United Launch Alliance in Decatur, Alabama. The Boeing-designed interim cryogenic propulsion stage is a liquid oxygen/liquid hydrogen-based system that will give Orion an extra punch of power on the first, uncrewed flight of the spacecraft with NASA's new rocket, the Space Launch System, in late 2018.

But even once we test this we will be looking at a total redo of the EDS stage for use going anywhere else with this very expensive rocket....

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#230 2018-01-21 21:07:41

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 11,540

Re: The SLS: too expensive for exploration?

We know that the ship to what should be keeps sliding to the right as it gets farther down the line for making use of it for moon missions or more... But this will not help either

NASA estimates that nearly 17,500 employees will be furloughed during a government shutdown, according to a shutdown plan published by the agency in November 2017. That is nearly 85% of the agency's workforce. Those furloughed who are working on experiments will not be allowed to touch them until after the shutdown, and by that point, they might have to start all over again.

Post made for what will introduce more delays.....not politics

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#231 2018-04-14 08:40:20

SpaceNut
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From: New Hampshire
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Posts: 11,540

Re: The SLS: too expensive for exploration?

EM-1 Update: Making progress, but still behind schedule
Exploration Mission-1 (EM-1) is currently expected to launch in 2020.
KSC is the final assembly and integration site where Orion prime contractor Lockheed Martin puts the whole spacecraft together for launch.

Sounds to me like a lot of feet dragging with each piece of the assembly.

update:
NASA’s realigning dual Mobile Launcher plan targets extra SLS Block 1 missions
written by Chris Bergin April 23, 2018

Originally, Exploration Mission -1 (EM-1) and Exploration Mission -2 (EM-2) were near-mirrors of each other, with an uncrewed Orion sent on a test flight “around” the Moon before the mission was repeated with a crewed Orion.

2018-04-22-194027.jpg

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#232 2018-05-13 14:51:27

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 11,540

Re: The SLS: too expensive for exploration?

The cost of a launch is directly tied to all of the heritage parts... so a switch over may not be a bad thing to help push Nasa...

SLS requires Advanced Boosters by flight nine due to lack of Shuttle heritage components

2018-05-08-201622.jpg

which means no more recovery....

NASA has issued a new Request For Information (RFI) that shows there is a deadline for the Space Launch System (SLS) to transition to “Advanced (Evolved) Boosters” no later than the ninth flight. This is due to a future obsolescence issue with the current booster design which relies on Shuttle heritage components of which there is only a limited amount of stock remaining. NASA intends to purchase another six SLS flight booster sets before the stock runs out, prior to moving to the Advanced Boosters.

2018-05-08-182957.jpg

It has always been in the planning for SLS to move to an Advanced Booster, partly in a requirement for its Block 2 rocket, that is required for Mars missions. The Block 2 is not expected to launch until the 2030s based on long-range NASA outlook manifests. Crewed missions to Mars with SLS have been projected internally as mid-to-late 2030s recently. Nearly six years ago, Dynetics, Inc. and Pratt & Whitney Rocketdyne (PWR) formed a team “to offer an affordable booster approach that meets the evolved capabilities of the SLS” – and presented their overview at the 63rd International Astronautical Congress, Naples, Italy in 2012.

Dynetics’ original proposal for liquid Advanced Boosters for SLS.

Their liquid booster approach – using the baseline of the famous Saturn V F-1 engines – claims they could advance SLS’ capability to launch payloads of 150mT to orbit.

Orbital ATK’s proposal – nicknamed the “Dark Knights” due to their black casings – builds on their booster legacy, with a motor that is “advanced” on several levels, by “provid(ing) NASA the capability for the SLS to achieve 130 mT capability – the baseline for SLS Block 2 – with significant margin, utilizing a booster that is 40 percent less expensive and 24 percent more reliable than the current SLS booster.

They are also looking at the dual launch as well...

NASA’s realigning dual Mobile Launcher plan targets extra SLS Block 1 missions

Block 1 performance capability for Europa Clipper may push the launch vehicle discussion into an uncomfortable debate, where SpaceX’s Falcon Heavy could force NASA’s hand based on the gulf of vehicle costs.  A brand-new Falcon Heavy for a high priority science mission would cost just over $100 million, whereas the latest estimates for SLS put the per-mission cost anywhere between $500 million (from NASA in 2013) to a range between $1.5 – $2.5 billion (conservative industry estimates in December 2017). If Europa Clipper does indeed stay on an SLS, as is currently mandated by Congressional law, the third flight of SLS would again be a Block 1 variant carrying the first crewed mission Orion.  A fourth Block 1 flight on the manifest may yet be needed before the EUS and ML-2 are ready.

plus possible other uses for such a large payload capability...

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#233 2018-05-14 13:31:18

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,952
Website

Re: The SLS: too expensive for exploration?

I had always thought that it would be Falcon-Heavy that outcompeted SLS for large payloads.  We built ISS from 15-ton payloads.  Falcon-Heavy will fling something like 60-65 tons to LEO.  SLS Block 1 is only about 70 tons to LEO.  Even SLS Block 2 is only 150 tons,  and from what you say,  won't fly until the 2030's at the earliest.  Per industry experts,  the SLS price tag for Block 1 is $1.5-2.5 B per launch,  from what you say.

Meanwhile,  Spacex supposedly (we'll see) will start limited flight testing of BFR's by 2019 or 2020.  If that goes well,  the BFR/BFS system will be flinging 150 tons of payload to LEO before SLS Block 2 ever flies,  and for a very tiny fraction of its cost.  Looks to me like the handwriting is on the wall,  although only a few letters of the first word,  so far. 

Not to mention Blue Origin and its plans for a similar heavy lifter.  Not sure,  but I think they're calling that concept "New Armstrong". 

Amazing what can be done when Congress isn't dictating the show almost solely for pork barrel politics and favored-contractor corporate welfare.  (THAT is why NASA cannot seem to do much any more.  That and plain old bureaucratic bloat.)

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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