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Biting Commentary about Infinity, and Beyond!

« Heinleinorama (Part Two) | Main | The Invasion That No One Noticed »

"You Can't Oversell It"

While reading Michael Belfiore's new book this weekend, I was struck by Brian Binnie's description of his X-Prize winning flight. Well, Jeff Foust has a report on a speech that Brian gave this past weekend, on what an amazing experience it will be. And if you can't oversell it, it makes it a double shame that Rocketplane may not be able to sell it at all.

Posted by Rand Simberg at July 09, 2007 07:22 AM
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Hi All,

I wonder how Richard Branson's parents (91 and 88) will handle 7 G's, not to mention Stephan Hawkings...

Posted by Thomas Matula at July 9, 2007 11:49 AM

Thomas from the link:
"Seven Gs lying flat is going to be the equivalent of 34 Gs sitting upright, which is what most normal people willing to expose themselves to this environment are comfortable with taking, he said. He later added that the seven Gs is not a constant value throughout the entire reentry period: the G profile is actually more like a bell curve that peaks at 7 Gs, with about 20 seconds where the G forces exceed 4 Gs."

I wouldn't be surprised if they could handle 3-4 g for 20 seconds, Stephen Hawkin as well (didn't he go through repeated 3+ g periods during his parabolic flights or was it less?). I hope all of them can.

Posted by Habitat Hermit at July 9, 2007 01:49 PM

Habitat

Some reference points. Max G's during a Shuttle flight to orbit and return are about 3-4 with the astronauts lying on their backs during launch.

I believe the Disney Mission Space ride has a max. G force around 2 or so. And they have lost a couple kids on it from heart problems since it opened.

So actually a force of 7 G's, even for a few seconds is very significant and far more then John Glenn endured on his Shuttle mission to orbit.

Also it appears from the article that Burt Rutan has abandoned the feathered tail approach used in SpaceShipOne. I wonder why given its was supposed to be the biggest break through of SpaceshipOne...

Posted by at July 9, 2007 04:38 PM

Also it appears from the article that Burt Rutan has abandoned the feathered tail approach used in SpaceShipOne.

Assuming the unnamed commenter is referring to the TSR article, I can't understand how such a conclusion could be drawn. Binnie never said that the feathering approach was being abandoned, and said that feathering was simpler than other approached, like BSC's variable ballistic coefficient concept announced last week.

Posted by Jeff Foust at July 10, 2007 03:07 PM

In reply to anonymous (Thomas?),

G force:

It will not be experienced as 7 g, please read up on the difference between horizontal and vertical (as experienced) g-force and also "eyes out"/"eyes in" (a seperate issue). The differences in position in regard to the g force has to be accounted for in all your examples, none of which have people lying down flat "on the floor" and some of which make a point out of applying g forces in just about all directions (rollercoasters etc.).

Feathering:

SS2 will be using feathering, the SS2 is a scaled up and refined/improved SS1. That's official and has been for a long time. Perhaps anonymous (Thomas?) is confusing speculation about Tier III or Rutan's/SC's involvement with t/Space and their launch system for the orbital CXV (which looks nothing like SS1/SS2) with the completely seperate issue of the suborbital WK2/SS2?

Armadillo, MSS, TGV, and Blue Origin, are all going for a HTHL design where they fire the rockets on descent to slow the vehicle down. The small (1-person) ARCA Stabilo uses parachutes on the seperated engine and payload modules. SS1/SS2 uses feathering and then gliding.

Feathering is/was a novel method for increasing drag to bleed off return speed that has additional advantages (self-stabilizing, easy passenger positioning in relation to g force, dual use of surfaces, relatively low "re-entry" heating issues, simplicity*). The big fuss: feathering was a new approach and it worked.

* the simplicity makes for easier redundancy if deemed necessary, in this case multiple independent hydraulic systems all working on the shared axis for shifting between feathered and glide mode. It wouldn't surprise me if the bigger SS2 has this.

Posted by Habitat Hermit at July 11, 2007 12:43 AM

Hi,

Yes, it seems names are not automatically saved on this blog as with Space Politics or Personal Spaceflight and I saw no way to fix it without reposting.

In regards to the examples, the Shuttle astronauts are on their backs in relation to the G forces from the Shuttles engines, so by your statement the 2-3 Gs they take are not really 2-3 Gs. Or the 3-4 Gs on a Soyuz re-entry with the Cosmonauts in acceleration couches with their backs to the g-forces of re-entry is less then they seem.

http://media.nasaexplores.com/lessons/03-067/9-12_article.pdf

Now as noted in this NASA article the G-forces on a Soyuz may go up to 9 Gs if there is a problem as on Expedition 6 with a shorten re-entry profile. Something that will also have to be kept in mind if the normal G-force on re-entry is already 7 Gs for Spaceshiptwo.

Which brings us to the question, wasnt the purpose of feathering the wing to reduce Gs on re-entry to make it easier? Or was it to just to reduce overall stress on the system?

Posted by Thomas Matula at July 11, 2007 01:50 PM

I invoke Carmack's defense. You can continue this conversation on your own Thomas as you obviously don't read what I write.

Posted by Habitat Hermit at July 11, 2007 10:30 PM

Habitat,

You didn't read what I wrote. A 7 G re-entry is higher then the Shuttle or Soyuz normally experiences. And higher then the 5 G Spaceshipone experienced.

So what is the advantage of the feathered wing if the passengers will still have to undergo more stress then existing orbital systems?

Vehicles may be designed to take more stress and be redundant. Human redesign is not an option and given the aging of the baby boomers, which seem to be the prime market for space tourism, makes you wonder if a 7 G design is wise.

Posted by Thomas Matula at July 11, 2007 10:45 PM


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