Europe's new space freighter prepares for maiden voyage
BY STEPHEN CLARK
Posted: March 5, 2008
Lauded as the most advanced spaceship ever built by Europeans, a robotic orbital freighter named Jules Verne will blast off from the Atlantic coast of South America this weekend to begin a three-week chase of the international space station.
Senior leaders representing the European Space Agency, Arianespace, contractors, and other international partners met Wednesday in a launch readiness review to clear the mission for flight.
"We are very pleased to smoothly pass this milestone four days before launch as scheduled," said John Ellwood, ESA ATV project manager. "Now we really feel to be ready, and our Russian and NASA partners have expressed the same confidence."
The 17-story rocket will be rolled from its assembly building to the ELA-3 launch pad in Kourou on Friday. Once the Ariane 5 completes the 1.7-mile trip, workers will connect electrical and fluid lines between the launcher and ground systems in preparation for the final countdown, which will kick off around midday Saturday.
See our detailed countdown timeline here.
Tipping the scales at 42,700 pounds, Jules Verne is more than two times heavier than any other spacecraft put into orbit by Europe. The first of five Automated Transfer Vehicles, the ship will deliver more than five tons of cargo to the station after going through a shakedown to make sure it is ready to approach the station.
The Ariane 5 rocket, a vehicle typically used to loft commercial communications satellites for launch provider Arianespace, was strengthened to handle the hefty mass. Engineers also had to make a few software changes because of the huge payload, and the launch will use an extended 56-foot payload fairing to house Jules Verne during the early minutes of flight.
If Endeavour lifts off Tuesday, the Ariane 5 will try again beginning Wednesday morning, according to Kirk Shireman, NASA deputy station program manager.
The shuttle and the ATV can't launch on the same day because both vehicles use S-band communications through NASA's Tracking and Data Relay Satellite System, Shireman said.
Riding nearly three million pounds of thrust, the Ariane 5 will fly northeast from the Guiana Space Center after liftoff, jettisoning its twin solid rocket boosters less than two-and-a-half minutes later and exhausting its first stage about nine minutes into the launch. Its storable propellant upper stage will fire twice before Jules Verne is cast free from the launcher.
See our detailed launch timeline here.
Jules Verne will be deployed in a 162-mile-high orbit inclined 51.6 degrees to the equator. After separation, mission responsibility will switch from Kourou to the ATV control center in Toulouse, France.
Jules Verne will begin its activation sequence moments after the Ariane 5 unleashes the spacecraft, turning on its electrical system, unfurling a communications antenna boom, and preparing for orbital operations.
"The ATV is switched on and the propulsion system is primed, the solar arrays are deployed, and we start the GPS, which provides the navigation in the first phase," said Bob Chesson, head of ESA's human spaceflight and exploration operations.
Waiting for station traffic to clear
Once controllers finish turning the ATV into a fully functional spaceship, attention will turn to its pursuit of the international space station. The first orbital "phasing" maneuver is scheduled for less than 12 hours after launch, beginning a three-week process to bring Jules Verne to the station's vicinity.
See our detailed mission timeline here.
The craft will spend its first ten days in space gradually shifting its orbit higher as ground controllers put the craft through a rigorous series of tests to confirm it is ready to approach the space station.
"The phasing period allows us to catch up with the space station and get it within our sights," Chesson said.
The comprehensive checkout will include an attitude control experiment, navigation tests using the ATV's GPS system, and the demonstration of a critical emergency thruster firing to be used if something goes awry during the final rendezvous.
The collision avoidance maneuver is an engine burn to push the ATV away from the station at a relative velocity of 11 miles per hour. That test is scheduled for approximately 0800 GMT (4:00 a.m. EDT) March 12.
Jules Verne will eventually arrive at a point about 1,200 miles in front of the space station by about March 19. The craft will hold in that orbit to wait out the shuttle Endeavour's visit to the station, which is scheduled to wrap up with an undocking on March 24.
Despite the conflict of Endeavour's mission, station managers opted to give the go-ahead for the ATV's launch.
"We'll launch as soon as ATV is ready, the launcher is ready, and the ground segment is ready," Ellwood said. "We then go to the space station and we have the option of immediately docking to the space station if the conditions are right, or we could loiter close to the space station."
The loitering philosophy will burn roughly 50 pounds of propellant per day, giving officials several options in their mission planning.
"We're actually more flexible in space than we are on the ground," said Alan Thirkettle, ESA space station program manager.
Demo Days pave way for docking
Once Endeavour departs the station, ESA controllers will resume putting Jules Verne through a checklist of pre-docking activities. The freighter will begin its push toward the station early on March 27, setting up for the first two "demo days" to showcase the craft's ability to autonomously fly in close proximity to the outpost.
"In each of those, we demonstrate various aspects of the ATV and prove that those features are working properly to ensure the safety of the vehicle and the station," Chesson said.
With ground controllers looking over the shoulder of Jules Verne, the craft will automatically fly toward the station through waypoints positioned at various distances from the complex. The ground team will give the "go" for the ATV to begin different phases of the rendezvous, but the ship's navigation and flight path will be generated on-board.
"The ATV control center monitors it all the time and we are able, if things go wrong, to interrupt in quite a significant way. If we spot a problem, for instance, we can initiate an escape maneuver and go off and do a thorough checkout of the spacecraft and even patch the software if necessary to allow us to make another attempt at rendezvous. There is a lot that the control center can do," Chesson said.
Initially positioned at an "interface point" 24 miles behind and three miles below the space station, Jules Verne will close within 2.2 miles during the first day of demonstrations, currently set for March 29. The ATV ground control center will then command the engines to fire in an escape maneuver to take the spacecraft to a safe orbit, wrapping up the nearly four-hour flight test.
The first demo day will test the long- and medium-range rendezvous navigation system, which relies on GPS antennas affixed to both the station and Jules Verne to produce accurate and timely range and closing rate information. The data is fed into the ATV's computers to plot a course toward the craft's next holding point.
A docking dress rehearsal is penciled in for March 31, assuming everything goes as planned on demo day one. Starting again from the interface point 24 miles behind and three miles below the space station, Jules Verne will move to a distance of 817 feet from the complex using GPS navigation.
At that point, the ATV's high-tech navigation system will begin using data from a suite of eye-like optical sensors attached to the forward end of the ship. Two videometers, working simultaneously with one in standby mode, will fire pulses of laser light toward the station one-to-ten times per second.
Acting as space mirrors, 26 reflectors positioned on the back end of the station's Zvezda service module will beam the laser beams back to the sensors on Jules Verne, creating unique light patterns captured on the ATV's cameras. The patterns will allow the ATV to autonomously determine its orientation, closing rate and distance from the space station.
Two other sensors known as telegoniometers will serve as watchdogs during the final rendezvous, Ellwood said.
The telegoniometers, similar to police radar guns, will also emit laser light at a different wavelength up to 10,000 times per second toward the reflectors. The light's travel time between Jules Verne and the station will determine range, while the direction of the station will be given by the angles of two built-in mirrors rotating to aim the laser at its target.
"We're the first vehicle which will completely automatically, using optical sensors, dock with the space station," Ellwood said.
The ATV's optical navigation system underwent a slate of tests on the ground to give engineers confidence the complicated sensors would work in space.
ESA tested the system using a mobile platform inside a nearly 2,000-foot-long building in France. The reflectors were attached to the platform and the ATV's optical sensors were placed on a robotic arm to imitate the spacecraft's movement.
"We did this very interesting and unique test of actually doing a real docking on the ground," Ellwood said.
"This is a unique technology that we've developed in Europe," Ellwood said. "We're really looking forward to seeing how it works."
The ATV is also fitted with Russia's Kurs rendezvous radar, a venerable system used to guide Soyuz and Progress capsules to automated dockings.
During the docking dress rehearsal, Jules Verne will follow a series of commands to demonstrate its ability to operate in tight quarters with the station.
"We will demonstrate the capability of ATV to hold, resume and retreat," Chesson said. "These are maneuvers that we could require if things don't go correctly during the rendezvous."
The ship will fly to a distance of less than 40 feet from the Zvezda docking port before pulling back to a point more than 60 feet away. Finally, the station's crew will give an escape command from inside the outpost to confirm they have the capability to abort a botched rendezvous.
In addition to the ground control center and astronauts aboard the station, the ATV's flight computers can also order an escape maneuver if they sense the rendezvous is going badly.
By the end of demo day two, officials expect the ATV to have proven all key features of its design, including GPS navigation and optical navigation, holds and retreats, ground- and crew-commanded escapes, and fine attitude control, Chesson said.
Engineers will also evaluate the performance of flight monitoring software overseeing the ATV's approach to the station. The system has the ability to abort operations if things go wrong.
The station mission management team will meet again on April 2 to give a formal "go" for docking if the ATV's demonstrations are successful.
"This will be a very exciting time, but we've really got to be sure that the vehicle is behaving exactly as we want," Ellwood said.
Officials expect to be able to remove the demonstrations from future ATV missions, reducing the launch-to-docking time to about 8 days, according to ESA.
Linking up with the station
"What we are doing actually amounts to a controlled collision with the space station - a very soft one," Chesson said.
Tentatively set for about 1420 GMT (10:20 a.m. EDT) April 3, Jules Verne's docking with the international space station must occur during a tight window stretching between March 30 and April 5.
Engineers are also concerned that the light could confuse Jules Verne's intricate sensors that rely on clear visual cues between the craft and reflectors on the space station.
A Soyuz spacecraft is scheduled to launch to the station with the Expedition 17 crew on April 8. The ATV will also be precluded from docking during the week-long crew handover, which is expected to end in mid-April.
Officials want to squeeze Jules Verne's docking before the Soyuz to avoid waiting up to two more weeks for the next rendezvous opportunity. The shuttle must also undock from the station early enough to allow the ATV to spend a week near the station for its rendezvous demonstrations.
"If the shuttle launches on the 11th or 12th (of March), we still have a shot at those demo days," Shireman said. "If the shuttle doesn't get off by the 12th, then what happens is the ATV will still launch, but it will wait until after the Soyuz joint mission is complete, and we'll do the demo days there."
Threading the needle between narrow docking windows will become even more common as the station continues to grow. At least five types of visiting vehicles could be flying to the station by the end of next year.
"There's quite a traffic flow going to the ISS. We're thinking about launching an air traffic controller here soon," Shireman joked.
Much like demo day two, the docking sequence will begin at the interface point before flying through the 2.2-mile hold point and arriving at the 817-foot mark behind the station, where navigation control will transition from GPS to optical instruments.
The Toulouse control center will evaluate the ATV's progress and issue "go" commands for the spacecraft to automatically move to hold points at roughly 65 feet and 30 feet, before giving approval for final approach and docking.
"We do a sort of dance with the space station. They're under their own control system. We're under our control system. We're like a pair dancing on the floor. We come in very, very slowly so that we do not collide," Ellwood said.
Russian cosmonaut Yuri Malenchenko and NASA astronaut Peggy Whitson will monitor the rendezvous from a control station inside Zvezda. Although station crews can take over manual control if the automatic docking system fails on Russian spacecraft, no such course of action exists for the ATV.
"All they can do is actually press a red button and send us away if they feel it would be unsafe," Ellwood said.
The station's crew will follow the approach through a network of video cameras and a live radio link beaming data from the ATV to their console in Zvezda.
Whitson and Malenchenko trained two weeks in Germany to prepare for Jules Verne's mission. Multiple failures must occur before the crew would be asked to intervene during docking, said Jean-Francois Clervoy, an ESA astronaut advising the ATV project.
Malenchenko, the prime crew member in charge of ATV docking operations, can order an abort until the ATV reaches three feet from the Zvezda rear port. After that point, an emergency maneuver could do more harm than good, according to Chesson.
Engine plumes from Jules Verne's thrusters could damage the station when they are fired at close range. The abort cutoff point also takes into account the crew's reaction time, Chesson said.
Jules Verne's Russian-built docking probe will contact the station at a closing speed of one-sixth of a mile per hour, engaging Zvezda's cone and forming a loose connection between the two craft.
The ATV's extended docking probe will retract a few minutes later to bring the two craft together. Electrical and fluid connectors will be mated, and eight latches will lock to create an airtight seal.
Delivering its cargo
After Jules Verne is firmly connected to Zvezda and controllers finish pressure checks in the docking system, the crew will enter the ship. The cargo carrier hatch, measuring about 31 inches in diameter, will be opened for the crew to access the craft's cache of supplies.
"This is when the ATV mission in support of the international space station really starts," Chesson said.
The ATV will also carry two 19th century manuscripts of Jules Verne novels for a commemorative ceremony on the station.
After removing the dry cargo, the crew will begin stuffing Jules Verne's logistics carrier with waste material.
"We'll be using it a bit like the cupboard," Ellwood said.
The crew will hook up lines to transfer nearly 600 pounds of water for drinking, cleaning and food rehydration. Astronauts must also manually open valves to move 46 pounds of oxygen into the station's air supply, according to an EADS fact sheet.
Once fresh water is pumped inside the station, the crew can transfer liquid waste back into the water tanks.
About 1,900 pounds of hydrazine and nitrogen tetroxide housed inside Jules Verne's refueling tanks will flow into Zvezda. The propellant will be used for the station's primary propulsion system on the Russian segment of the complex.
The ATV will exhaust about 60 percent of its own 12,900-pound fuel supply during its flight to the station, leaving about 5,000 pounds of propellant to raise the station's altitude, steer the complex clear of orbital debris, and provide attitude control when the outpost's gyroscopes are down. Jules Verne must also keep a fuel reserve for the craft's suicidal de-orbit burn at the end of the mission.
Engineers on the ground will control refueling and re-boost operations.
All told, Jules Verne carries about 10,100 pounds of supplies for the station, including dry cargo and fluids.
After spending about four months at the international space station, Jules Verne will back away from the complex in the first week of August. The ATV is designed to stay at the station for up to six months, and officials could decide to extend the mission until October, according to an ESA spokesperson.
"That fiery end of the ATV mission really concludes the operations of Jules Verne," Chesson said.
The risks of automated dockings
ESA officials say they have worked incessantly to decrease the mission's potential risk to the station and its crew, especially since Jules Verne is a first-of-a-kind spacecraft flying to such an important destination.
Similar to technology used on NASA's DART satellite and the Pentagon's Orbital Express mission, the optical sensors on the ATV are the ship's prime source of navigation information during the final approach sequence to the station.
DART's 2005 mission, designed to operate without any input from the ground, ended in failure due to a cascading list of consequences stemming from a late change in the craft's software. The computer improperly processed navigation data from DART's GPS and optical sensors, causing the spacecraft to lose its orientation and go off course.
"It wasn't looked at across the entire system to see the effect of that change across the entire system," Suffredini said. "It's a lesson for us all to keep in mind whenever we are dealing with complicated spacecraft like this."
The U.S. military's Orbital Express mission successfully demonstrated autonomous rendezvous and docking using a visual guidance sensor last year, but like the ATV, controllers were actively keyed into the process through each step.
"DART was a totally automated vehicle. We turned it on and sent it on its way, and sure enough it had an interesting life. That is not the case with the ATV," Suffredini said.
"It is automated, so it knows what it's supposed to do, but along the way, particularly on this flight, it's going to take certain steps and stop. We're going to look at the data, ensure it is acting the way we expect it to act and we can implement an abort and have it fly away from the space station while we figure out whatever issue that we were worried about at the time," Suffredini said.
Suffredini said all station partners were consulted regarding ATV safety issues. The partners all signed off on the mission's risk, and control centers in Houston and Moscow will track the rendezvous, he said.
"It is a first time, but I think with all of the work that's been done on the ground and with the demonstration that's being done on orbit, and the fact that in the end we're using the docking mechanism of the Russian segment, so the final thing is a proven system. The combination of all of those things gives us a sufficient feeling of confidence that this is a working vehicle," Thirkettle said.
Suffredini, Thirkettle's NASA counterpart, agreed: "We talked a long time early in the program about whether or not we needed to try to create a target for the ATV to dock to, and we agreed with this approach to ensuring that we will fully understand what the spacecraft is actually going to do in orbit, and that we practice these specific aborts or escape scenarios to ensure that they would work, that approaching the ISS on its first flight was a safe thing to do."
"We'll have a bigger smile on our face when it's actually achieved, of course," Thirkettle said.