#Orion at JPL/Armstrong (Part 5)

START WITH PART 1 OF THIS SERIES BY CLICKING HERE.

One of NASA’s most important missions for the future of human space exploration doesn’t—at least initially—call for astronauts. NASA is currently planning a deep space mission known as Asteroid Redirect Robotic Mission or, in NASA-speak, ARRM. This approach is in keeping with tradition at NASA; robotic missions have always preceded humans into space. Before Neil Armstrong and Buzz Aldrin touched down on the lunar surface, the Ranger and Surveyor probes had photographed the Moon’s surface and demonstrated the feasibility of lunar touchdown. Robotic efforts already underway on Mars and involves orbiting satellites and rovers.

ARRM Asteroid Capture (NASA)
ARRM Asteroid Capture (NASA)

ARRM is an ambitious program to visit an asteroid and either bring back a small, but complete, asteroid (Plan A) or touchdown on a much larger asteroid and return a boulder (Plan B). At the recent Orion/EFT-1 NASA Social, an event jointly hosted by JPL and NASA Dryden, Doug had the opportunity to listen to Brian K. Muirhead, JPL Chief Engineer and ARRM Pre-project Manager, describe the ARRM program.

The essence of the ARRM program is to visit a Near Earth Object and bring all or part of it back to a stable orbit—referred to as a distant retrograde orbit—in the Earth-Moon system. One candidate asteroid is Itokawa, a Mars-crossing—meaning that it crosses Mars’s path so that this asteroid’s orbit is sometimes inside and sometimes outside of Mars’s orbit—asteroid that was visited in 2005 by the Japanese Hayabusa spacecraft.

Plan A involves bringing back an entire asteroid. In order to do this, the robotic spacecraft would match orbit with the asteroid and capture it with a bag made of Kapton. The image gives a sense of how this might happen. Kapton has a long history of use in space missions, and Kapton blankets are often the material of choice for thermal insulation in space suits and spacecraft on deep space missions.

ARRM (NASA)
ARRM (NASA)

Plan B, which calls for the return of a boulder from a large asteroid, will use a capture system—somewhat like a robotic arm or grappling device—to secure the boulder and lift it off of the asteroid.

In either case, mission length is estimated to be approximately six years, with a spacecraft launch in 2019 and a return of the asteroid (or boulder from an asteroid) sometime during 2025. There is one shorter-duration mission profile. It’s possible that the Plan A mission designed to return the entirety of asteroid BD 2009 could return by 2023.

Why will this be such a lengthy mission? The small amount of thrust delivered by ion electric propulsion systems also accounts for the lengthy mission times. One of the enabling technologies for ARRM is High-Power Solar Electric Propulsion (HPSEP). HPSEP is a variation of ion thruster-based electric propulsion, a technology with which NASA has been rapidly gaining experience over the past fifteen years. Ion thrusters make use of electrical charge to accelerate ions across an electric field. This form of propulsion can create rocket engine exhausts that are traveling approximately ten times faster that the exhaust of chemical rocket propellants. (In fact, the exhaust propellant of an ion thruster is moving at about 40 kilometers/second or 90,000 miles/hour.) At the same time, the ion thrusters make very efficient use of their propellant. Xenon is NASA’s ion thruster propellant of choice.

Doug at JPL (NASA photo)
Doug at JPL (NASA photo)

While the exhaust from an ion thruster is moving very fast, not much is being moved. In 1998, NASA launched the Deep Space-1 spacecraft, powered by the NSTAR ion thruster. At its peak performance, the propellant flow rate of the NSTAR engine is measured in milligrams per second (mg/s). The NSTAR ion engine produces approximately one-hundred million times less thrust than the Saturn F1. In fact, the force generated by the NSTAR engine has been likened to the effort required to hold a single sheet of paper. The NSTAR thruster required 2.3 KW of electric power to be supplied to the engine. This was accomplished through solar power arrays attached to the spacecraft. The planned ARRM mission will require a scaled-up version of the Deep Space-1 systems.

It’s only once the asteroid is returned to the Earth-Moon system that the human exploration side of program takes over. The ARRM project calls for the asteroid to be placed into a lunar Distant Retrograde Orbit (DRO). The key advantage of a DRO versus LEO (low-earth orbit), which was the first suggestion, is that NASA simulations have shown that a DRO is stable for at least 100 years, and Muirhead pointed out during his presentation that a DRO is probably good for longer timeframes.

After the asteroid has been placed in orbit, NASA’s plan is to use astronauts onboard the Orion spacecraft to visit the asteroid for 22-25 day missions. In order to fully investigate the asteroid, NASA wants to accomplish five days of extravehicular activities—spacewalks—by astronauts.

Imporantly, NASA believes that both the mission length and complexity will serve as an excellent proof of concept for human exploration of Mars. NASA has an ambitious future planned for humans and robots, and the recent Orion/EFT-1 NASA Social was an excellent way to learn about some of those programs.

Imporantly, NASA believes that both the mission length and complexity will serve as an excellent proof of concept for human exploration of Mars. NASA has an ambitious future planned for humans and robots, and the recent Orion/EFT-1 NASA Social was an excellent way to learn about some of those programs.

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