Thinking Big about Space Telescopes

Right: A cutaway diagram of the large monolithic space telescope shows that most of it is empty space, leaving designers plenty of margin in equipping the systems and instrument modules. (NASA)

NASA's next moon rocket is still on the drawing board, but already scientists are dreaming up big new things to do with it.

"The Ares V rocket will be able to launch missions whose volume or mass or both can be handled no other way," says Philip Stahl, an internationally respected optical engineer now at NASA's Marshall Space Flight Center. Maybe, he says, we should use it "to launch big space telescopes."
How big? Consider the following: Ares V will be able to place almost 130,000 kg (284,000 lbs; 8% more than the Saturn V rocket of the 1960s) into low Earth orbit. Designed to deliver cargo to the Moon, the rocket would be large enough to carry primary mirrors 8+ meters wide. For comparison, Hubble's mirror measures 2.4 m.

"How does a typical astrophysicist work?" Stahl asks. "He builds a giant telescope on top of a mountain and uses it for decades, and every few months or years he swaps out instruments or does other upgrades to keep it going."

The Hubble Space Telescope operates in this fashion, with the space shuttle doing the servicing and Earth-orbit playing the role of mountain peak.

But Stahl wants to go beyond Earth orbit, far beyond, to the L2 Sun-Earth Lagrange point.
A Lagrange point is, basically, a parking spot in space. If you put a spacecraft at a Sun-Earth Lagrange point, it remains in a fixed position relative to the Sun and Earth. 18th-century mathematician Josef Lagrange showed that there are five such points, illustrated in the diagram.
L1, located 1.5 million km sunward of Earth, is a good place for solar observatories. The Solar and Heliospheric Observatory (SOHO), for example, is there now and enjoys a 24/7 view of the sun.

L2 lies in the opposite direction, 1.5 million km above the nightside of Earth. A key advantage of L2 is that the Sun, Earth and Moon are concentrated in one small part of the sky, giving any telescope located there a wide and unobstructed view of deep space. The Wilkinson Microwave Anisotropy Probe (WMAP) is stationed at L2 and others will eventually join it.

"L2 is a place in space where we want to place a lot of telescopes," Stahl continues. So "why don't we treat it as a mountaintop?" with the telescope's satellite bus providing all the services of a real mountaintop facility.

Thus, Stahl, Marc Postman of the Space Telescope Science Institute, and others within the space science community are thinking big.

Wish-list missions for the Ares V range from a 150-meter-wide (492 ft) radio telescope dish to detect whispers from deep space to a 5-meter cube of super-pure water encased in light detectors to assay cosmic rays by their light flashes as they crash through the water. An optical telescope with a primary mirror up to 8 m (26 ft.) in diameter could search star populations in the Milky Way and nearby galaxies for the "fossil record" of their evolution. It could also hunt for "Earthshine spectra," faint signs of life in the light reflected by exoplanets.

The resolution of the telescope's images would be more than three times sharper than those of Hubble. More important, the mirror would see about 11 times fainter than Hubble because the area of the mirror would be 11 times greater.

Until now, such a mirror was too big to consider. The next-generation James Webb Space Telescope -- also headed for L2 -- was regarded as the path for future large space telescopes. Its 6.5-m primary mirror will consist of carefully folded segments that precisely align once on station. But future Ares V payload shrouds up to 12 m (39.4 ft) have been envisioned by NASA planners. That allows Stahl to consider an off-the-shelf mirror, like the single-piece, 8-m (26.2 ft) primaries in the ground-based Gemini telescopes.

While increasing size, the Ares V would decrease risk. "The constraints of current launch vehicles place risks on technical performance, cost, and schedule to get a lot out of a small package," Stahl explains. The generous size and mass afforded by the Ares V all but eliminates those constraints for most payloads.

He also sees servicing as a key element.

"Why design for 10 to 15 years?" Stahl asks. "Let's design so you can swap the instruments periodically and go for 50 years." The bus section -- controls and instruments -- will be small enough that replacements could be sent by smaller launch vehicles and equipped to replace all the serviceable components and start a new scientific observing campaign.
In Postman's words, that would "make L2 the ultimate astronomical summit."

source: science.nasa.gov

Throttling Back to the Moon

Above: Multiple images on the left are pictures of the CECE engine at different throttle levels.

Above: Apollo 11's Lunar Module, the Eagle.

July 16, 2007

Accelerating from 0 to 60 then slowing down for a stop light is no problem for an ordinary automobile. But if you were piloting a rocketship, it wouldn't be so easy. Most rocket engines are designed to burn full-on (liftoff!) or full-off (coasting through space) with no in-between. And that can be a problem--namely, how do you land this thing?

Throttling is crucial for a planetary lander. Descending from orbit is a unique balancing act, cutting engine power as the lander losses mass through the engine exhaust that slows it, until landing pads just kiss the surface. For a lunar landing, velocity drops from almost 4,000 mph to 0 in about one hour.

The Apollo Lunar Module (LM) descent engine, the all-time throttling champ, did it perfectly on six landings in 1969-72. It could throttle from 10,125 lbs down to 1,250 lbs. It was also a simple engine, burning corrosive fuel and oxidizer that ignited on contact, and fed by pressurized tanks, eliminating the need for pumps.

NASA is heading back to the Moon in the next decade, and "we want to put more mass down on the lunar surface than Apollo did. That means we need a higher-performing engine," says engineer Tony Kim of NASA's Marshall Space Flight Center. "The Apollo Lunar Module descent engine was very good, very reliable, but it doesn't have the performance we need for future exploration."

To investigate technologies for a next-generation lunar lander, engineers at two NASA centers--the Marshall Space Flight Center in Alabama and the Glenn Research Center in Ohio--are supporting Pratt & Whitney Rocketdyne in developing the Common Extensible Cryogenic Engine--"CECE" for short.

At CECE's core is the RL10 engine that boosted seven Surveyor robot landers to the Moon in 1966-68, then flew dozens of other missions for more than 2.2 million seconds of operations (almost 26 days) and 718 in-space firings. The RL10 is a far more powerful and complex beast than the Apollo LM engine. It burns hydrogen and oxygen that are stored as supercold liquids in insulated tanks. These are not only high-energy propellants, but also environmentally friendly compared to the corrosive fuel of the original LM.

Now the engine is being asked to demonstrate something new: throttle from 100 percent of its 13,800-lb thrust to 10 percent on command for a human-rated spacecraft. But making it throttle is not as simple as pushing the gas pedal in and out. Like most rocket engines, the RL10 was designed for full power. Almost like a living organism, changes in one area are felt through the entire body. For example, at low power, liquid hydrogen can slow and vaporize in the coolant lines, possibly stalling the engine.

In Phase 1 Demo 1 tests, "we were able to get the engine modified and show that throttling is possible, though cautiously," Kim says. CECE racked up 932 seconds of firing time in eight tests, though some were cut short "because we are experimenting."

The principal challenge was "chugging." Something was causing the engine to vibrate 100 times per second. Pratt & Whitney Rocketdyne conducted a "Demo 1.5" to investigate and isolate the problem: It turns out oxygen vapors were forming on the injector plate and inhibiting normal flow at lower throttle levels.

"We're considering modifications to the injector and valves to improve performance," Kim says. Already, CECE has demonstrated stable combustion (no chugging) down to 5-to-1 and operability (some chugging) at 11-to-1 throttle ratios.

CECE's not ready for space, Kim emphasizes, but it is an important testbed to develop technology. "This work has the potential to influence design of the next lunar lander."

source: www.science.nasa.gov

Approaches to Creativity

There are two main strands to technical creativity: programmed thinking and lateral thinking. Programmed thinking relies on logical or structured ways of creating a new product or service. Examples of this approach are Morphological Analysis and the Reframing Matrix.

The other main strand uses 'Lateral Thinking'. Examples of this are Brainstorming, Random Input and Provocation. Lateral Thinking has been developed and popularized by Edward de Bono, whose books you can find in the appropriate articles.

Programmed Thinking & Lateral Thinking
Lateral thinking recognizes that our brains are pattern recognition systems, and that they do not function like computers. It takes years of training before we learn to do simple arithmetic - something that computers do very easily. On the other hand, we can instantly recognize patterns such as faces, language, and handwriting. The only computers that begin to be able to do these things do it by modeling the way that human brain cells work . Even then, computers will need to become more powerful before they approach our ability to handle patterns.

The benefit of good pattern recognition is that we can recognize objects and situations very quickly. Imagine how much time would be wasted if you had to do a full analysis every time you came across a cylindrical canister of effervescent fluid. Most people would just open their can of fizzy drink. Without pattern recognition we would starve or be eaten. We could not cross the road safely.

Unfortunately, we get stuck in our patterns. We tend to think within them. Solutions we develop are based on previous solutions to similar problems. Normally it does not occur to us to use solutions belonging to other patterns.

We use lateral thinking techniques to break out of this patterned way of thinking.

Lateral thinking techniques help us to come up with startling, brilliant and original solutions to problems and opportunities.

It is important to point out that each type of approach has its strength. Logical, disciplined thinking is enormously effective in making products and services better. It can, however, only go so far before all practical improvements have been carried out. Lateral thinking can generate completely new concepts and ideas, and brilliant improvements to existing systems. In the wrong place, however, it can be sterile or unnecessarily disruptive.

source: mindtools.com