Wednesday, April 4, 2012

Flying Formation - Around the Moon at 3,600 MPH

The act of two or more aircraft flying together in a disciplined, synchronized manner is one of the cornerstones of military aviation, as well as just about any organized air show. But as amazing as the U.S. Navy's elite Blue Angels or the U.S. Air Force's Thunderbirds are to behold, they remain essentially landlocked, anchored if you will, to our planet and its tenuous atmosphere. What if you could take the level of precision of these great aviators to, say, the moon? 

"Our job is to ensure our two GRAIL spacecraft are flying a very, very accurate trail formation in lunar orbit," said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We need to do this so our scientists can get the data they need." 

Essentially, trail formation means one aircraft (or spacecraft in this case), follows directly behind the other. Ebb and Flow, the twins of NASA's GRAIL (Gravity Recovery And Interior Laboratory) mission, are by no means the first to synch up altitude and "air" speed while zipping over the craters, mountains, hills and rills of Earth's natural satellite. That honor goes to the crew of Apollo 10, who in May 1969 performed a dress rehearsal for the first lunar landing. But as accurate as the astronauts aboard lunar module "Snoopy" and command module "Charlie Brown" were in their piloting, it is hard to imagine they could keep as exacting a position as Ebb and Flow. "It is an apples and oranges comparison," said Lehman. "Lunar formation in Apollo was about getting a crew to the lunar surface, returning to lunar orbit and docking, so they could get back safely to Earth. For GRAIL, the formation flying is about the science, and that is why we have to make our measurements so precisely." 

As the GRAIL twins fly over areas of greater and lesser gravity at 3,600 mph (5,800 kilometers per hour), surface features such as mountains and craters, and masses hidden beneath the lunar surface, can influence the distance between the two spacecraft ever so slightly.
How slight a distance change can be measured by the science instrument beaming invisible microwaves back and forth between Ebb and Flow? 

How about one-tenth of one micron? Another way to put it is that the GRAIL twins can detect a change in their position down to one half of a human hair (0.000004 inches, or 0.00001 centimeters). For those of you who are hematologists or vampires (we are not judging here), any change in separation between the two twins greater than one half of a red corpuscle will be duly noted aboard the spacecraft's memory chips for later downlinking to Earth. Working together, Ebb and Flow will make these measurements while flying over the entirety of the lunar surface. 

This begs the question, why would scientists care about a change of distance between two spacecraft as infinitesimal as half a red corpuscle a quarter million miles from Earth?
"Mighty oaks from little acorns grow – even in lunar orbit," said Maria Zuber, principal investigator of the GRAIL mission from the Massachusetts Institute of Technology, Cambridge. "From the data collected during these minute distance changes between spacecraft, we will be able to generate an incredibly high-resolution map of the moon's gravitational field. From that, we will be able to understand what goes on below the lunar surface in unprecedented detail, which will in turn increase our knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today."
Getting the GRAIL twins into a hyper-accurate formation from a quarter million miles away gave the team quite a challenge. Launched together on Sept. 10, 2011, Ebb and Flow went their separate ways soon after entering space. Three-and-a-half months and 2.5 million miles (4 million kilometers) later, Ebb entered lunar orbit. Flow followed the next day (New Year's Day 2012). 

"Being in lunar orbit is one thing, being in the right lunar orbit for science can be something else entirely," said Joe Beerer, GRAIL's mission manager from JPL. "The twins initial orbit carried them as close to the lunar surface as 56 miles (90 kilometers) and as far out as 5,197 miles (8,363 kilometers), and each revolution took approximately 11.5 hours to complete. They had to go from that to a science orbit of 15 by 53 miles (24.5 by 86 kilometers) and took all of 114 minutes to complete."
To reduce and refine Ebb and Flow's orbits efficiently and precisely required the GRAIL team to plan and execute a series of trajectory modification burns for each spacecraft. And each maneuver had to be just right. 

"Because each one of these maneuvers was so important, we did a lot of planning and testing for each," said Beerer. "Over eight weeks, we did nine maneuvers with Ebb and 10 with Flow to establish the science formation. We would literally be watching our screens for a signal telling us about an Ebb rocket burn, then go into a meeting about the next burn for Flow. Our schedule was very full." 

Today, the calendar for GRAIL's flight team remains a busy one with the day-to-day operations of keeping NASA's lunar twins in synch. But as busy as the team gets, they still have time to peer skyward.
"Next time you look up and see the moon, you might want to take a second and think about our two little spacecraft flying formation, zooming from pole to pole at 3,600 mph," said Lehman. "They're up there, working together, flying together, getting the data our scientists need. As far as I'm concerned, they're putting on quite a show." 

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the GRAIL mission for NASA's Science Mission Directorate, Washington. The Massachusetts Institute of Technology, Cambridge, is home to the mission's principal investigator, Maria Zuber. The GRAIL mission is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. JPL is a division of the California Institute of Technology in Pasadena.

Synchronized NASA and ESA flights across Arctic Ocean - a success!

By Malcolm Davidson/ESA and Michael Studinger/NASA
Arctic sea-ice from the NASA P-3 (NASA/M. Studinger)
Monday April 2 has been much anticipated by the teams in Thule, Greenland (NASA) and Alert, Canada (ESA). While the objectives for the day were clear – jointly fly with all available planes beneath CryoSat’s early morning pass over the Arctic Ocean – the execution of such flights is and always will be a challenge. 
Flying joint multi-plane missions is a rather daunting task. Departure and rendezvous times and locations need to be calculated and maintained to ensure that the instruments on the different planes will see the same sea-ice floes below (these move after all), flight altitudes need to be established and maintained for safety reasons, instruments need to be warmed up and ready ‘in-time’, somewhat grumpy firefighters need to be coaxed out to the airstrip ahead of working hours to support an early departure and the list goes on.
With both teams committed to the flights, the first task early this morning was to check the weather forecast for the day. These proved to be good with temperatures of –29°C (–20°F) and generally clear skies; but not ideal! Some rather worrying cloud formations featured near the coast in satellite images.
NASA P-3 cockpit (NASA/M. Studinger)
Nevertheless, after a quick phone call between the NASA and ESA coordinators (at a time before most people have yet to reach for their mug of morning coffee) the decision was made: it's a go.
From then on it there was a flurry of activity on both sides, pilots warmed up their planes, instrument teams checked out their instruments, flight plans were programmed into the onboard computers and so on.

Twin Otter takes off
The NASA P-3 plane was the first to go out, leaving Thule a full hour before the two ESA planes located closer to the track. On the tarmac in Alert there was the first casualty of the day – despite heroic efforts the EM-bird ice-thickness instrument could not be coaxed into life. The die was cast – the second Twin-Otter plane would have to go it alone and meet up with the NASA P-3.

NASA’s sea-ice mission plan for April 2 (yellow). We teamed up with ESA at 10520 north of Alert. (NASA/M. Studinger)
Around 07:30 (local time) the CryoSat satellite – always on schedule – ripped above the Arctic Ocean taking about one minute to race along the 500-km (310 mile) transect that would later take several hours of plane time to cover.
At 08:00 both the ESA and NASA planes reached the edge of the Arctic Ocean almost simultaneously and headed across the sea ice flying exactly along the same line that CryoSat had just covered. The timing was so good that, for the first time, there was visual contact between the planes, a remarkable achievement!
The image below, which is a DMS mosaic from Eric Fraim shows one of the many leads we saw from the NASA P-3 today with a variety of different types of sea ice.

DMS mosaic of lead in the sea ice (NASA/DMS/E. Fraim)
The rest of the day turned out very well indeed. The clouds that had worried the teams in the morning only formed only a thin band near the coast. The rest of the line out on the ocean was clear and beautifully lit by the oblique Arctic Sun. All the onboard scientific instruments on both planes worked well so that by the end of the day it was clear that the day had been a success.
By joining forces both the ESA and NASA teams collected a highly valuable dataset that will benefit the scientific achievements of ESA’s CryoSat and NASA’s future ICESat-2 mission to better monitor sea ice from space.

Space Is My Mistress

Seeing as how April is National Poetry Month….
Space is My Mistress
Space is my Mistress,
and she beckons my return.
Since our departure I think of you
and yearn to fly across the heavens arm in arm.
I marvel at your figure,
defined by the edges of continents.
You gaze at me with turquoise eyes,
perhaps mistaken for ocean atolls.
You tease me to fall into your bosom,
sculptured by tectonic rifts,
only to move away as if playing some tantalizing game.
Time and time we turn together,
through day, and night, and day,
repeating encounters every 90 minutes with a freshness,
as if we have never seen our faces before.
We stroll outside together,
enveloped by naked cosmos,
filled with desire to be one.
So close,
you sense my every breath,
which masks your stare through visor haze.
We dance on the swirls of cloud tops,
while skirting the islands of blue.
You know my heart beats fast for you.
Oh, Space is my mistress,
and when our orbits coincide,
we will once again make streaks of aurora across the sky.