Nh - The Launch Thread, Godspeed little one Options

[djellison]

I thought it was time, with the Atlas V about to roll out - for a new thread for NH for the launch etc.

Someone asked over at the HZ just how NH can go so fast, this was my reply....

How do you get a spacecraft to Jupiter in under a year? Easy. Make it very very light, and put it on a very very big rocket. The config of Atlas V rocket being used to launch NH (551 - 5m fairing, 5 solids, and one engine on the Centaur stage ) would typically put 8,670kg into GTO or 20,520 into LEO.
New Horizons is 478kg, and it's Star 48B 3rd stage is 2,137kg - so instead of hauling 20 tons, this vehicle is hauling about 2.5 tons thus you get a HUGE velocity out of it. AND, once it's done that, you have the final kick of the 48B, 591 thousand kgs-s (thus accelerating is all a further 3.5 - 4km/s ball park speed, if my maths is right)
At launch - the vehicle is 573,160kg. NH is 0.083% of it.
Imagine the Apollo entry capsule on top of a Saturn V...tiny tiny tiny... that was 5,800 kg on a 3,038,500kg rocket - 0.191% - more than double that percentage of NH. The cutaway's are almost comical, with this tiny gold-clad box on an enormous vehicle.
Basically - it's a LOT of rocket, and not a lot of payload.
For comparison, look how much fuss was made of Stardust that entered so quickly. It took >16 hrs to get from the distance of the moon to Utah. NH makes that journey in 9 hours
One thing the NH mission is not short of, is superlatives.

I'm not one for good luck charms (although I'll eat peanuts during a Martian EDL with the best of them), but this mission has been so long in coming, that it deserves every ounce of luck it can have - the best, most accurate launch possible, the cleanest checkout, and incident free cruise to Jupiter.

Goodluck and Godspeed little one, we're with you every step of the way.

Doug
PS - Alan, you're a credit to your field, spending so much time answering questions and writing the PI Perspectives, it's been a hell of a journey!

[djellison]

It's not uncommon for LV's to turn, quite a lot, after SRB sep. If you look at the rocket-cam views from Spirit and Opportunity - you can see, once SRB sep has occured, the vehicle turns quite a lot. I'm not sure why, but perhaps it's because they have to be in a particular direction for SRB-jet for range reasons, and THEN can pitch to the launch heading they want?

Doug

[Ames]

It's not uncommon for LV's to turn, quite a lot, after SRB sep.  If you look at the rocket-cam views from Spirit and Opportunity - you can see, once SRB sep has occured, the vehicle turns quite a lot.  I'm not sure why, but perhaps it's because they have to be in a particular direction for SRB-jet for range reasons, and THEN can pitch to the launch heading they want?

Doug

I think the rationale behind this is that early on, what you want to do is to get out of the dense atmosphere (high drag) as quickly as possible and straight up vertically (whilst augmented with the SRB's) is the quickest way.
Then when drag becomes less of an issue you want to build speed to reach orbital velocity and horizontal (tangential) is the way to go. Obviously they can't launch straight up because of safety reasons.
So you usually see a gradual transition from vertical to horizontal, but NH nodded! it was VERY noticeable and may heart sank for a moment.

But I think the Shuttle does it the best. I watched the first launch on TV and thought it was literally going belly up, which actually it was!

It was nice to see the telemetry from the Centaur upper stage. Another heart stopping moment when I looked back and it was firing and pointing directly at the Indian Ocean - some sort of sling shot manoeuvre I presume.

Nick

[just-nick]

I think the rationale behind this is that early on, what you want to do is to get out of the dense atmosphere (high drag) as quickly as possible and straight up vertically (whilst augmented with the SRB's) is the quickest way.
Then when drag becomes less of an issue you want to build speed to reach orbital velocity and horizontal (tangential) is the way to go. Obviously they can't launch straight up because of safety reasons.

This also involves the dynamic pressure issue -- the aero forces acting on the rocket. If you try to build up actual tangential velocity too soon (as opposed to getting up, up, up out of the atmosphere), you risk getting into aero loads that can tear a flimsy old rocket apart. So by going UP early, you get out of the atmosphere more quickly and also actually keep the overall speed down because gravity is fighting you more directly. Then you turn the corner and, now that the air is thin, start cracking on.

I read that when Boeing launched the first Delta 4H, they stayed vertical for an unusually long time for just this reason -- getting some altitude before starting to build too much velocity. As a result, all that LH2 was just hanging out over the cape for a lot longer than was typical. So a lot of non-essential personnel were evacuated.

This dynamic pressure thing is quite significant -- look at the throttle curve for NH's RD180, down to 64% just seconds after launch according to Aviation Week, all just to keep the speed in check until the atmosphere starts to go away.

--Nick (other)

[tty]

This also involves the dynamic pressure issue -- the aero forces acting on the rocket.  If you try to build up actual tangential velocity too soon (as opposed to getting up, up, up out of the atmosphere), you risk getting into aero loads that can tear a flimsy old rocket apart.  So by going UP early, you get out of the atmosphere more quickly and also actually keep the overall speed down because gravity is fighting you more directly.  Then you turn the corner and, now that the air is thin, start cracking on.

Very true. If something bad happens during a launch it is very often near "Max Q", i e maximum dynamic pressure. This applied to both Challenger and Columbia for example. Max Q typically occurs at something like Mach 2 and 50,000 feet.
I suspect that it was this "Max Q" problem that made Burt Rutan select the seemingly unnecessarily complicated air-launch concept for Spaceship One. By launching the ship that high he actually kept the dynamic pressure within limits where off the shelf rudder actuators etc could be used, despite a Mach 3+ top speed. This may have been a factor in the rather extreme feathering concept - to loose as much kinetic energy as possible high up where the air is thin.

tty

[just-nick]

Very true. If something bad happens during a launch it is very often near "Max Q", i e maximum dynamic pressure.

Yeah, learning about dynamic pressure, what it is and why it is important, was a big part of my growth as a rocket engineer. Growth from drawing rockets in the margins of my notebooks in school (elementary school) to drawing rockets in the margins of my notebooks in school after doing a great deal of math first (graduate school).

Its worth pointing out I'm a masters of education program...

--Nick