Page last updated at 16:59 GMT, Monday, 20 July 2009 17:59 UK

Flying on the wings of 'Eagle'

By Jonathan Fildes
Technology reporter, BBC News


How the new Altair system would land astronauts back on the Moon

"We wanted it to be a bit more Star Wars or Star Trek but the physics gets in the way," says John Connolly, chief architect of Nasa's new Altair Moon Lander.

The spacecraft, part of the US space agency's Constellation programme, is the vehicle that Nasa hopes will carry man to the surface of the Moon by 2020.

Despite Mr Connolly's fantasies about its design, prototypes of the craft bear a striking resemblance to the Eagle lander which carried Neil Armstrong and Buzz Aldrin to the lunar surface 40 years ago.

"That was an ugly, spidery spacecraft," he says. "But the Apollo engineers got a lot of things right."

Like the Eagle, Altair will be delivered into orbit by a heavy-lift rocket (the Ares V, currently under development) and then ferried on towards the Moon by a command module.

And like its predecessor it is a two-stage vehicle: a descent and an ascent stage.

The large descent module - including the fragile looking legs - consists largely of an engine and propellant tanks.

The smaller ascent module - on top of the vehicle - contains the life support systems and the engine required to get the astronauts back to an orbiting module; another throwback to the Apollo days.

But if it looks like Eagle, that is no surprise. The Altair team have been poring over the old design blueprints and have even drafted in some of the old Apollo engineers.

"We ask them a lot of questions," said Mr Connolly.

Even the lander's name has echoes of the Eagle. Altair is the brightest star in the constellation Aquila, Latin for Eagle.

But there are also key differences.

For starters, the new craft is much larger and is a multi-role vehicle, able to deliver astronauts or cargo to the Moon's surface.

In a standard mission, it will be able to deliver four astronauts to the lunar surface, compared with the Eagle's two.

Altair Lander
Altair has been designed as a multi-use vehicle

The module acts as living quarters for the crew and features an airlock, meaning that the whole cabin does not need to be depressurised every time an astronaut exits the vehicle.

It also has an additional advantage.

"We talked to the Apollo astronauts and they had a real problem with dust in the cabin," said Mr Connolly.

"The airlock allows us control the dust - dusty space suits can be kept out of the cabin - and it also allows us to split the crew's operations."

In the new lander, for example, two astronauts could remain inside whilst two others explore outside.

The airlock - because of its weight - is left behind on the Moon's surface with the descent stage when the astronauts are ready to leave.

Other configurations of the new lander allow it to act as a lunar outpost, sustaining a crew for more than six months, or as a cargo truck, shipping more than 14 tonnes of material to the surface. These option are critical for Nasa's plans to set up a base on the moon as a staging post for exploration on Mars.

The design margins for Eagle were very thin
John Connolly

All the vehicles use a common descent stage, with different configurations of craft on top depending on the mission.

However, one of the main differences to Eagle is the craft's ability to land almost anywhere on the lunar surface.

"Apollo was restricted to mid latitudes and broad daylight," explained Justin Vican, part of a team at the Draper Laboratory in Boston, US, which is developing a new landing system for Altair.

"They could only land under optimal conditions."

Looking down

The Autonomous precision Landing Hazard Avoidance Technology (Alhat) project at Draper Labs - the place where the first Apollo Guidance Computers were designed - aims to overcome these limitations.

"One of the hardest spots to land is somewhere like the South Pole," said Mr Vican. "Odds are you are going to be landing in total darkness."

Alhat will basically allow the astronauts to see in the dark.

Eagle Lander
The physics of spaceflight determines the shape of the lunar landers

It will use a suite of sensors and technologies such as a flash Lidar (Light Detection and Ranging)

"It's like a sonar but with light," explained Mr Vican.

The system gives the astronauts very high resolution topographical images of the surface.

"From space you can see the big obstacles. The real danger is if you land on a rock three feet high."

The team behind Alhat aim to have a system that can detect objects "about the size of a basketball" along with steep or cratered terrain.

When the system picks up a hazard, it warns the pilot and allows them to choose a new and precise landing spot on the fly.

It is an example of how technology is reducing the risk of space flight.

"The design margins for Eagle were very thin," said Mr Connolly. "Altair should be safer."

The spacecraft is currently on its third design, but Mr Connolly says there will be likely be a "dozen more" before it is set in stone and the blueprints turned over to an industrial partner to construct.

However, there is still a question whether it will get that far.

Currently, the Obama administration is undertaking a review of Nasa's manned space activities. The Augustine review, as it is known, is due to report back in August.

"Nasa is playing its part [in the review]," he says. "We feel good. If there is an option of going to the Moon, we will need a lander."

And if it does get the go-ahead, does he think a new era of manned lunar exploration will capture people's imaginations in the same way as Apollo?

"I think it will do in a different way," he says. "With communications technology, it will be a very personal experience. But still very exciting."

Composite image of moon landers
Apollo 'Eagle' lunar lander
Crew size: 2
Surface duration: 3 days
Landing site capability:
Near side, equatorial
Stages: 2
Overall height: 7.04m (23.1ft)
Width at tanks: 4.22m (13.8ft)
Width at footpads: 9.45m (31ft)
Ascent stage mass: 4,805kg (10,571lbs)
Descent stage mass: 11,666kg (25,665lbs)
Descent engine thrust: 44.1Kn (9,900lbf)
Altair lunar lander
Crew size: 4
Surface duration: 7-210 days
Landing site capability:
Stages: 2
Overall height: 9.9m (32.5ft)
Width at tanks: 8.8m (28.9ft)
Width at footpads: 14.9m (49ft)
Ascent stage mass: 6,141kg (13,510lbs)
Descent stage mass: 37,045kg (81,500lbs)
Descent engine thrust: 83.0Kn (18,650lbf)

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