CAPE
CANAVERAL, Fla. — When astronauts return to the moon by 2020, they will do so
following a familiar path and flying in a cone-shaped capsule that echoes the
"good old days" of Project Apollo.
But the
skin-deep similarities between Apollo's Command Module and Constellation's
Orion spacecraft are far outnumbered by differences - more like
improvements — that NASA's 50 years of spaceflight experience make possible.
"We've
learned a lot, but we still have a lot of questions," said Bret Drake, Chief
Architect in the System Engineering and Integration Office for Constellation at
the Johnson Space Center in Houston.
For
example, the best Apollo could offer by 1972's final lunar excursion was a
two-man crew lingering for about three days at a landing site that was
generally near the moon's equator.
Constellation
is shooting for a means to land anywhere on the moon and eventually grow the
capability to build up a permanent presence at one site, likely near one of the
poles, Drake said.
"We're
trying to evolve a capability, right out of the box, where we're going to have
four-member crews staying on the surface for seven days," Drake said. "But
eventually we'll get to the point where we have four crewmembers on the surface
for 180 days."
That
potential still is more than a decade away, and though the fine details of what
all the hardware is going to look like continue to evolve, the picture of how
the United States will go
back to the moon is coming into focus.
"Functionally,
physics drives you in a lot of the same directions we went through in
Apollo," Drake said. "We're doing a lot more with the systems than we were
with Apollo."
Skin
Deep Beauty
To start,
that means the Orion spacecraft will be shaped like a cone, Drake said.
When
determining the best shape to deal with the speeds and heat of reentry
encountered by a spacecraft returning from the moon, the laws of physics are
the same in the 21st Century as they were in the 20th Century.
So from a
distance the Orion spacecraft looks almost identical to the Apollo
Command Module. Up close the differences become more apparent, especially
the size.
Orion is
now set to be 16.5 feet (5 meters) in diameter and 10.8 feet (3.3 meters). It
will weigh about 31,000 pounds (14,000 kg) empty and have a habitable volume of
692 cubic feet (11 cubic meters).
Apollo's
Command Module by comparison: A diameter of 12.8 feet (3.9 meters) and a height
of 11.4 feet (3.47 meters). Total dry weight was 12,787 pounds (5,800 kg) and
its crew cabin volume was 218 cubic feet (6.17 cubic meters).
Both
spacecraft had or will have an attached Service Module that will have a single
large engine fed by storable propellants and contain storage and bays to
support the main cabin systems.
Both Apollo
and Orion's Service Module will have batteries and electricity generating fuel
cells, but the Orion also has a pair of solar arrays to help keep the vehicle
powered during its intended long stay in lunar orbit.
And that
brings to light some of the key difference between the Apollo and Orion mission
scenarios, or more simply, the paths they will follow from the Earth to the Moon.
From the
Earth to the Moon
During
Apollo, a single three-stage Saturn V Moon rocket carried the crew, Command
Service Module and the Lunar Module into Earth orbit. After one orbit the
Saturn V's third stage was re-ignited and sent Apollo toward the Moon.
After
discarding the third stage on the way to the Moon, the Apollo spacecraft
entered lunar orbit. At the appropriate time, two of the three crewmen boarded
the Lunar Module and went down to the surface, leaving the third crewman in the
Command Module.
The plan
for Constellation, as it stands now, is to launch a four-person crew in an
Orion spacecraft atop an Ares I launch vehicle from the Kennedy Space Center
into Earth orbit, where it will wait up to four days, Drake said.
Ninety
minutes after the Ares I launch, a heavy-lift
Ares V rocket is to launch the Altair lunar landing spacecraft and an Earth
Departure Stage into Earth orbit for a same day rendezvous and docking with the
Orion capsule.
The joined
spacecraft will remain in Earth orbit for up to four days while waiting for the
Moon to orbit into the right position when the launch window for a Trans-Lunar
Injection opens up. Then the combined spacecraft will blast their way toward
the Moon.
After
discarding the Earth Departure Stage, the Altair lunar lander's rocket engine —
powered by liquid hydrogen and liquid oxygen — will brake the spacecraft into
orbit around the moon.
This is
different from Apollo, which relied on the Service Module's main service
propulsion system engine for the same job.
Location
is Everything
Although
plans for the first mission or so may change, Drake said the baseline plan is
for all four astronauts to board Altair for the trip to the lunar surface,
leaving an empty Orion spacecraft to circle the moon on its own.
That's a
big difference from Apollo, which left one astronaut in the Command Module to
keep that spacecraft healthy and the crewmember busy with "bird's eye" science
observations of the surface.
As for the
selection of a lunar landing site, during Apollo a variety of sites were
explored, all generally near the moon's equator. For Constellation, a single
site will be selected, likely near one of the poles.
Among the
reasons, according to Drake:
- With each
landing NASA will leave equipment there that can be joined with other
hardware to build up a permanent station on the surface.
- It may be
possible to establish this site in a place on the Moon where there is
always sunlight, which can help with generating electricity and
maintaining the correct thermal conditions with the surface hardware.
- It is
also possible that a crater near the poles that remains in constant
darkness may hide water ice, which can be broken down into hydrogen and
oxygen for use in powering fuel cells, producing rocket propellant and
making drinking water.
Under
the Hood
Systems
inside Apollo versus Orion also will be very different.
While
Apollo had a switch for everything, Orion will have glass cockpit displays and
touch-sensitive screens that can be programmed on the fly.
While
Apollo relied on computers with less power and memory than a digital toy found
inside a cereal box, Orion will have the latest computers plugged into an open
architecture that allows upgrades to software and hardware.
While
Apollo used a pure oxygen atmosphere in space, Orion will use a nitrogen-oxygen
mixture at reduced pressure to make it easier for spacewalking or Moonwalking
astronauts to depart the spacecraft.
And while
Orion's heat shield will use an ablative material and parachutes for a
splashdown in the water like Apollo, unlike Apollo there continues to be talk
about how much of an Orion spacecraft can be reused after flying, Drake said.
"We have a
lot of options on the table," Drake said of the entire Orion system.
Jim Banke is a veteran aerospace commentator
and consultant based in Cape Canaveral, Fla.
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