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twitter.com/erdayastronaut/status/1574418932579987456

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I donít recall exactly what is the thing thatís the slowest operation, but I donít think they can get it back to the pad in time for that whole launch window. Calling @ChrisG_NSF / @SciGuySpace / @Alexphysics13, is October for sure out?

https://twitter.com/sciguyspace/status/1574419554012479488

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NASA has not said so officially, but I don't see how they can roll back, get ensconced in the VAB, perform FTS work and other tasks, and somehow roll out again by Oct. 21. If they get yet another FTS extension, maybe? But I think October is highly doubtful.

Edit: Alex has it

https://twitter.com/Alexphysics13/status/1574419947144495104

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Today Dr. Z said on an interview that if a rollback happened they'd be looking at November for the next opportunity. I think it's mostly because of the timing that it would probably only let them do an opportunity, maybe two at most, right at the end of October. Not worth the try
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I hesitate to call VASIMR a known technology.  It's never flown, and those are at theoretical power levels never tested.   No power source to power it at that high power has ever flown or been tested.


Both are firmly within our current technological capabilitiies. With appropriate funding, both could be flown with less than 10 years of development.

VASIMIR has completed high-power long-duration test fires in the past couple of years, last year they did an 88 hour burn of the VX-200SS engine. NASA is pushing for development of space rated nuclear reactors.

The main point is that sub 60 day Mars transits are possible.

88 hours at 80kw.  80kw is off by at least 3 orders of magnitude.

Doing the math, that is a total of 25GJ.  That's a Raptor firing for a mere 25 seconds.

To accelerate a 200T vehicle to 10km/sec requires 10TJ.   On an 88 hour burn that requires 32MJ/sec or 32MW.  So yes, almost 3 orders of magnitude.

I have yet to find a multi-hour vasimr burn in the megawatt range.

(NERVA was 1.2GW, about the same as a Raptor, albeit at 20x or more the static mass)


http://parabolicarc.com/2021/07/23/vasimr-vx-200ss-plasma-rocket-completes-record-88-hour-high-power-endurance-test/

"Electric  rockets operating above 50 kW/thruster are  considered “high-power.”    LOL I guess you can define "high power" that way.

It's high powered for an electric thruster.  In comparison, the NEXT Ion thruster operates at up to 7.7 kW.  Some test fires with the previous iteration of the VASIMR engine were over 200 kW.

Yes, you'd want a larger version for a large crewed vehicle, although the burn would be much longer, could even be continuous, so you wouldn't need a huge 32 MW engine.  The AdAstra conceptual Mars transit vehicle has a cluster of three 4 MW engines.

The point still stands that with sufficient funding, this could be developed within 10 years.  Sub 60 day trips to Mars is quite feasibly within the realm of possibility.

Nope.

To get to Mars in 60 days would take ~460MW of Starship sized vehicle (1000t propellant, 200t payload + dry vehicle mass) at a constant ISP of ~6500s. If you switched variable ISP (Vasimr like) and optimized for power use you could maybe get it down to 250MW electric power. If you shortened the burn, double the thrust and halved the ISP (so you'd accelerate/decelerate half the time, and coast another half) you'd maybe get somewhat better power, likely 150MWe. This is SciFi power density (squeezing 150MWe power plant into such mass budget is SciFi).

To merely meet chemical transit time of 3.5 month's you'd need about 60MWe at constant ISP of 3200s (so cuttable to 30MWe at variable ISP constatnt burn or 20MWe half time burn at a halved ISP). Or rather than going thorugh all the pains of 60MWe (or 20MWe) power plant and its radiators (thermal power optimizes at 4x electric power for space use; get rid of 80 to 240MW of heat) just use chemical:

* Do 4.5km/s burn from plain old VLEO. Thanks to the effect named after Mr Oberth you get 5.45km/s Vinf (4.5km/s  includes whole 3.124km/s climb-out from Earth's gravity well and 1.276km/s hyperbolic burn; the later translates into 5.45Vinf)
* Fly for 3.5 months (average window)
* Arrive at Mars at 10.56km/s just before entry interface (this is not Vinf, this is entry interface + 0.2km/s for equatorial rotation speed)
* Do 2.2km/s burn to slow down just before Mars aerocapture, so you enter the atmosphere at 8.16km/s relative speed (again, 0.2km came from equatorial rotation speed).
* Do ~4g aerocapture pass (4g is dictated by negative lift necessary to follow Mars curvature at Starship's 60į AoA; could be lowered to ~2.5g if AoA were lowered to 45į)
* Slow down to somewhere around 4.5 to 4.7km/s surface relative, jump out of the atmosphere, do once around, correct at apoapsis for a precise reentry and then execute EDL by the next periapis.

That's about what's feasible using Starship-like vehicle, with larger header tanks (for storing slow-down propellant) and with an advanced heatshield able to withstand 3-4x peak heating of LEO reentry. But this is much closer to available tech than 20MWe not to mention 150MWe space reactors.
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Missions To The Moon (HSF) / Re: Moon to Mars Objectives
« Last post by yg1968 on Today at 03:16 pm »
I just noticed that NASA already had exploration objectives in HEOMD-001 but they haven't been updated since 2017 (before Artemis was announced):
https://www.nasa.gov/sites/default/files/atoms/files/heomd-001-heomd-exploration-objectives-revision-a-cr-08032017.pdf

See also slides 23 and 24 of this presentation for more on HEOMD-001:
https://www.nasa.gov/sites/default/files/atoms/files/2-human_exploration_operations_committee_report.pdf
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Concerning LEO users of Starlink and Kuiper, I donít think the responders here are considering the actual physical issues of a LEO constellation servicing LEO users. If the constellation is only 150 km higher than the user, there will be gaps in coverage, unless the constellation is specifically designed for coverage of LEO users.
ISL links are point-to-point. Each LEO user is a single specific additional "satellite" in the constellation as far as the rest of the constellation is concerned, and there are very few of these orbiting users. At any given time, some particular ISL link on some particular comms satellite is programmed to point to the orbiting user and it dedicated to that user. this responsibility is handed off to some other other satellite as the orbits cause the relative positions to change. This is completely different than the way a satellite's radio beams to the Earth's surface work. It is identical to the way ISL creates point-to-point links within the constellation.

Does the satellite rotate to point the ISL laser at the user?
(This is an abstract description that may not be accurate in detail for Starlink)
You cannot have a true ISL network unless multiple satellites have at least three active links. With only two links, you can have a chain or a loop but not a network.
To serve users on the ground, the satellite's main antenna array must point toward Earth and its orientation is highly constrained. The satellite is not free to rotate arbitrarily. In general, this means the satellite has a "front" end that points along its orbit. This in turn means a satellite can keep one ISL pointed at the satellite ahead of it in its orbit and another ISL pointed at the one behind it, with only a small amount of pointing gimbal range of motion since these satellites do not move much at all with respect to each other. Thus, each orbit forms an ISL ring.  At least some satellites (realistically, all of them) will have two or more additional ISLs that have a much larger range of motion. These can point to satellites in other orbits. Those satellites do move with respect to each other, a lot. Thus, the network topology is continuously changing, but in a highly predictable way.

With this hardware, a few satellites in the each ring must provide network ISL to other rings (more is better) but there are spare ISLs that can point to "user" ISL spacecraft.

This entire elaborate dance of ISLs requires tight coordination, down to the millisecond, as the links are made and broken. A user spacecraft will need at least two gimballed ISL lasers to maintain continuous communication in a make-before-break manner.

The laser ISL hardware is basically a small telescope, probably about 4 cm in diameter.

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New Physics for Space Technology / Re: Woodward Effect - Thread 2
« Last post by SeeShells on Today at 03:10 pm »
For the simple minded among us - are you saying that you have visually detected real thrust from a Mach Effect device? The Holy Grail, so to speak?

Was the visual lifting video in your presentation an example of real, visually observable thrust? Or was it an example of a false positive?
Hi M.E.T.,

There are few simple-minded people here. :) Much respect for those who are here.

This is not my effort alone, and it appears that we are seeing real thrust events. We know Mach Effects are buried within Newtonian mechanics, which can, and will muddy your test results. The keys were along with the fiber optic philtec sensors, and the introduction of multi-point video motion monitoring during runs, including acceleration, velocity, momentum, kinetic energy, the center of mass, etc. of the device. This was coupled with confirming results with thrust levels on 3 different test beds in 2 labs.

This is a great question about the video and I wondered how it affected the results. It lead me to tear down the vertical counterbalanced torsion arm and go to a frictionless air-bearing, (great observation BTW). In the video with the device sitting on the vertical counterbalanced torsion arm, it looks like it is just rising a little as it pushes and re-centers into the support structure. False positive? Maybe, maybe not. Tests with a horizontal torsion arm in a vacuum chamber say no. The only way to be sure it's not is to test on a frictionless air-bearing and replace the stretchy polyester supports with Kevlar or G-glass supports which have the advantage of holding up better in a full vacuum. Those tests have started and this will be the 4th style test bed. Did you see the very first results on the air sled in the presentation?

My Very Best,
Michelle

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I think that it easily *could have become* the pacing item, if a full EIS was required or unexpected mitigation were added that needed more work before launches.

Now that it's been issued and the contents are known, it proved not to be the pacing item.
Well, yes and no but also yes LOL. I think SpaceX took advantage of the permitting delay to upgrade Starship with newer, more powerful Raptors and a different design of Starship and Super Heavy, and readying this new vehicle for flight has become the pacing item for launch, no longer permitting delays.

If the permitting delays had never happened, itís possible they couldíve pressed to flight with Raptor 1/1.5 and gotten to orbit earlier. But the flip side is the permitting delay wasnít at all a total waste because they could choose to improve Raptor and Starship and the launch tower a lot in the meantime.
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Missions To The Moon (HSF) / Re: Artemis 1 Discussion Thread
« Last post by crandles57 on Today at 03:05 pm »
Perhaps worth tracking how NHC's 120 hour wind speed probabilities change with each update from
https://www.nhc.noaa.gov/refresh/graphics_at4+shtml/145630.shtml?tswind120#contents

Eyeball of map for Cape Canaveral 8am EDT 26th Sept update:

____________________8am 24__2pm 24__8pm 24__2am 25_8am 25_2pm 25_8pm 25_2am 26_8am 26
Trop stm 1 min >=39mph: 33%___25%____24%____25%____32%___35%___46%____54%___54%
50 knot 1 Min >= 58 mph: 9%____6%_____5%_____5%_____7%____7%____11%____17%___13%
Hurricn 1 min >= 74 mph: <5%___<5%____<5%___<5%____<5%___<5%__<5%____7%____<5%

Risks reducing but decision made
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https://twitter.com/jdeshetler/status/1574235302805192704

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Slow motion shot of engine ignitions on the rear of Delta IV Heavy - NROL-91 as it successfully launched from Vandenberg SFB yesterday.
@NASASpaceflight
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Concerning LEO users of Starlink and Kuiper, I donít think the responders here are considering the actual physical issues of a LEO constellation servicing LEO users. If the constellation is only 150 km higher than the user, there will be gaps in coverage, unless the constellation is specifically designed for coverage of LEO users.
Tell that to Jared Isaacman.

An argument from authority!

Perhaps there isnít a requirement for continuous coverage, maybe the occasional burst of laser comm will be enough.
No argument from authority implied, you just seemed to keep dodging the fact that Polaris Dawn intends to demonstrate direct Starlink laser comm to LEO Dragon.
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Missions To The Moon (HSF) / Re: Artemis 1 Discussion Thread
« Last post by whitelancer64 on Today at 03:02 pm »
Two more questions: they've decided now but are not actually rolling back until 11pm (ET). Does that leave a window to change the decision if the NHC updates today move the storm away from KSC, or is this decision final and something else is causing the wait until 11pm?

Also, upon rolling back, will they do more leak-related inspections or will it just be "get the SLS out of the way of the hurricane, change FTS batteries, back to pad"? And if it's the latter, how soon can it be back on the pad?

There's a whole bunch of on-pad work that needs to be completed to secure SLS to the ML before the roll-back can begin.

They can (and most likely will) do further leak checks in the VAB, but that is done with gaseous helium.  The problems are happening when the QD plate is contracting from thermal cooling from the cryogenic liquid hydrogen.  Flowing liquid hydrogen through the system can only be done out on the pad.

I would presume they will do a full checkout of the SLS in the VAB, as well as fix anything that needs fixing, before they will roll it out. The pad itself would also need to be checked for any wind related damages before roll out.
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