FITZGERALD: Hey guys. I recently had an opportunity to talk to the researchers and
engineers over at HIAD, which stands for the Hypersonic Inflatable
Aerodynamic Decelerator, or what I like to call 'space brakes.'
It's very interesting technology. It's something that I would've never thought of
having an inflatable structure in space to slow down
spacecraft. GIERSCH: Inflatable structures, in the general sense, is becoming very popular.
ALLEN: Yeah. But I understand it a little more in the hab, because we
do have decelerators now. We use parachutes. How does this... Are we still using parachutes?
Is this a different thing altogether? FITZGERALD: Well, we're using inflatable structures
in addition to parachutes because what happens is that the
size of the spacecraft can only get so big. And
after it gets larger, you need a decelerator that's going to go ahead and slow it
down. GIERSCH: So, with the inflatables, that structure can go beyond the spacecraft and slow... FITZGERALD: Exactly.
ALLEN: And I'm just assuming -- I'm sure we'll find out in the story -- that the inflatables weigh
less than, you know, the normal... yeah, ok. FITZGERALD: That's the big... that's the big difference.
ALLEN: Partnering with those inflatable moon walk things that kids use
as part of a technology partnership, or is that separate? FITZGERALD: You're talking
about moon bounces? ALLEN: Yeah. Moon bounces. Yeah. FITZGERALD: Nah, I doubt it.
GIERSCH: Alright, let's go check out the segment on HIAD.
FITZGERALD: I'm here with Neil Cheatwood, principle investigator for HIAD.
Exactly what is HIAD? CHEATWOOD: Well, HIAD stands for Hypersonic
Inflatable Aerodynamic Decelerator. And let me break that down for you.
When we go to other worlds, we have to launch from Earth and then we have to decelerate
And we can do that either propulsively -- like we did at the moon, with the lunar module --
and use just engines to slow us down. But if it's a world with an atmosphere, then
it makes sense to make use of that atmosphere and that atmospheric drag. And so what we
do is we actually wrap our payload -- you know, what we're taking to the surface of the planet --
we wrap that in what we call an aeroshell. We're currently limited to
the size of aeroshell that we can do based on the rocket size. So our aeroshell has to
fit inside that rocket shroud. So the idea is, if we
could deploy a larger aeroshell out of a given rocket,
then we could take down more mass and actually get more payload to the surface of
Mars, or Venus or wherever. What we're working on here is a
hypersonic version of that where we deploy outside the atmosphere. But then we have to
handle that heat pulse, the high deceleration pulse that we see when we go into the
atmosphere. So that is a hypersonic inflatable aerodynamic decelerator.
FITZGERALD: One of the big part of HIAD is the inflatable structure. So tell us a little bit about
how it is constructed. HUGHES: Ok. Well, what we have here is a stacked
torus. And the way you make a torus is you braid
a tube, and then that tube then has a liner, a silicone liner, inside of it
and you inflate the tube and it becomes a torus.
And if you stack the tori together so they intersect, or interfere, with each other they become a pretty rigid
structure, as you can see over here. We have to protect the structure from the heat of reentry, so
we apply a thermal protection blanket. The outside is a nextel fabric
which we've quilted together. And I'll take this ring off and show you the way it's
constructed. The fabric itself keeps the integrity of the outer structure.
Then we have an insulator ply, which you can see is this
powdery yellow surface in here. That takes the outer surface heat
and knocks it down to a temperature that the bladder can tolerate. And we have these gas
barriers beneath it that prevents inflow of the hot gases. The hot gases on the outside
are wanting to drive to the low pressure. Behind there, in the wake region
of the aeroshell, is a very low pressure. So the pressure on the front wants to drive through, so we have to put a gas barrier
behind it. And this is a test sample for running in the 8-Foot High Temperature Tunnel.
We've instrumented it with some thermocouples so we can see what the various temperatures are in between
the layers. And we can match that up to the models that we've done for prediction. It's to see
how well the TPS performs. FITZGERALD: Could you explain a little bit more about why you would
use an inflatable reentry system versus the
old, rigid thermal heat shield? CHEATWOOD: We've been to Mars, as an example.
The first time we went was 1976, with Project Viking. And there was a big
technology development program for Project Viking. They developed a TPS material
called SLA-561V, which is Super-Lightweight Ablator
561V, for Viking. We've actually used that on every successful Mars
mission since then. And here we are in 2011. And so we've been using all that technology
all these years, but we've been sending more and more stuff each time.
So the payloads are getting bigger. And, in actuality, our next mission to
Mars is the biggest payload we've sent there, the Mars Science Laboratory. And
we had to switch our TPS materials because it was getting so heavy. And even
with that, we can only land at what was below sea level
at Mars because we're just coming in too fast; we're too heavy.
So the idea is to make a larger drag device so that we could land
that same mass at a higher altitude or take more mass to the surface. So it's all about
size. Size does matter. FITZGERALD: Your next text coming up is IRVE 3
Tell me about that. HUGHES: IRVE 3 is another suborbital flight. We've had IRVE 2, which
was our first successful demonstrator. IRVE 3, we've increased the mass of the payload
so that we can get about twice the heating applied to the aeroshell, and
this time, we're going to require a TPS. Last time, we just had the fabric to
show how well it stowed and whether it survived the rigors of packing. This time,
we need to demonstrate that we can pack with the insulator. And the insulator
is a fairly low density material, so we need to make sure that we can pack it down
very tightly. And it's also a fairly delicate material, so we need to make sure that it doesn't
fall apart when we package it and then, later, deploy it. FITZGERALD: Neil, tell me about
where we might be able to use this technology. CHEATWOOD: We can use the aeroshells where we have a sensible atmosphere.
When I say 'sensible atmosphere,' it has to be enough that... really, means anything.
The moon does not have a sensible atmosphere. That's why we landed using retro
propulsion. Mars has what I call a 'poor excuse' of an atmosphere.
It's very thin. It's the most challenging destination for us because it's actually
too thick an atmosphere to ignore -- we don't want to just take rockets
and land on the surface; it's not very efficient. But it's so thin, it's like a
hundred thousand feet here at Earth. You know, it's very challenging. But we can use
this technology at Mars. We could use it for Earth return. We could bring stuff back
from the Space Station. We could bring stuff back from the moon. We can use it at other
atmospheres, like Venus, the gas giants -- Jupiter, Saturn, Uranus, Neptune.
Titan, which is the largest moon around Saturn, has a very thick atmosphere.
So it could be used at any of those locations. HUGHES: We've done some studies and demonstrated
that these are enabling technologies for... way out there
where we're doing a manned Mars mission. They're talking about landing
40 metric tons of payload on Mars. Right now, there's absolutely no way to do that.
Well these aeroshells are potentially a technology that will allow us to do that.
once we figure out a way to get 40 metric tons to Mars orbit safely... that's another challenge.
FITZGERALD: That's a big challege. HUGHES: That's a big challege. FITZGERALD: But you're up to the challenge? HUGHES: Oh yeah, we're on it.
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