Activities conducted using spacecraft have become a ubiquitous part of our society. From monitoring hurricanes to measuring the ozone layer to a host of defense-related missions, U.S. government agencies today rely heavily on satellites and aerospace technology to conduct their day-to-day activities. But how are satellites conceived, designed, produced and deployed?
NASA describes a spacecraft as “a vehicle or device designed for travel or operation outside the Earth’s atmosphere.” A satellite is described as “a type of spacecraft that orbits the Earth, the moon or another celestial body.” In this series, we will use the terms spacecraft and satellite interchangeably.
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Planning for the launch and deployment of a spacecraft begins in the earliest days of its conception, when a customer is still defining mission requirements on the “back of a napkin.” How large the spacecraft will be, what orbit it will occupy, and how much shock and dynamic loading it can sustain during liftoff all help determine the type of launch vehicle that can deliver it most effectively to orbit.
“Typically, we’re procuring the launch vehicle as a commercial service for the government or working with them to figure out what launch vehicle they plan to provide,” says Will Whalen, a launch system integration (LSI) specialist with Northrop Grumman.
Either way, Whalen adds, the LSI team is working with a customer team and the contractor’s space vehicle and mission payload team very early in the proposal development phase to define the most appropriate — and most competitive — launch vehicle. Launch and launch vehicle costs can make up 10 to 30% of the mission value, so it’s very important to get it right.
Creating the Right Match
After a contractor secures a satellite contract, its LSI team begins working closely with the space vehicle team and the launch vehicle provider to ensure a good match — mechanically and electrically — between the space vehicle, or satellite, and the launch vehicle.
“It’s critical that all stakeholders in the launch and deployment process work together from day one,” emphasizes Whalen.
The LSI team works with the launch vehicle provider to define the electrical and mechanical interfaces between the satellite and launch vehicle, the dynamic forces that the satellite and the upper stage will experience, and the details of the separation sequence, adds Whalen. It’s important, for example, that the second stage provide sufficient thrust and stability to steer and control the satellite safely through the suborbital and separation phases of launch.
The LSI team also coordinates early in the satellite development process, Whalen explains, with U.S. government entities —typically U.S. Air Force — that will need to support the launch. For military launches, for example, the Air Force provides satellite fueling services on the ground, plus radar systems and ground control stations that track the satellite during launch and deployment.
Shipping for Safety
After the satellite has been completed, it is shipped to its launch site, typically two to four months before launch depending on how much work the contractor team expects to do at the launch site.
Most U.S. satellites are launched from Cape Canaveral Air Force Station or Kennedy Space Center in Florida, or Vandenberg Air Force Base in California. Satellites are either shipped by air (a few hours) or truck (a week or longer).
“Whenever possible, we transport satellites by air because it’s faster, involves less risk, and avoids delays that can occur if we ship an oversize container by truck on normal U.S. highways,” explains Whalen. “Sometimes our customer arranges for us to use a specialty government transport system such as a C-17 Globemaster or C-5 Galaxy aircraft.”
Coming Clean
At the launch site, the satellite is brought into a processing facility that contains a series of progressively cleaner rooms.
The first stop is an airlock where the shipping container is cleaned of all its road or air transport grime. Next is a high bay where the satellite is erected, lifted out of its shipping container, and placed on a processing stand that will allow integration and test (I&T) specialists to work on the satellite at different levels.
Checking Reality
After the I&T team connects its test sets and charges the satellite’s batteries — they are shipped in a low state of charge to ensure safety and preserve battery life — it begins a carefully scripted series of tests.
“During this phase of launch preparation, we activate the space vehicle, check out its payloads, and make sure that all of its subsystems — command and data handling, propulsion, attitude control etc. — are functioning the way we expect,” says Whalen. “We want the specialists who designed and tested these systems in the factory to review the data and validate one last time that the data looks good and that none of our subsystems have been damaged in transit.”
Preparing for Launch
After the space vehicle has been shown to be operating correctly, and before it is fueled, the launch preparation team simulates connecting the satellite to the Air Force Space Command Network (AFSCN), the communication link used during launch, deployment and on-orbit checkout. The AFSCN also provides a backup channel for sending commands or receiving telemetry should the satellite’s primary communications link become unavailable during normal on-orbit operations.
The final phases of the contractor’s launch preparation include integrating the satellite mechanically with its separation system, and installing a special nose cone called the payload fairing around that entire assembly. The fairing protects the spacecraft against aerodynamic pressure and heating during launch and its ascent through the atmosphere. With the space vehicle contractor in observation mode only, the launch vehicle provider then integrates the fairing-enclosed payload with the launch vehicle.
Counting Down
And then the countdown to launch begins. The countdown period is normally 12 hours or less.
Prior to countdown, all of the launch stakeholders, including contractors, customers and base authorities, meet for a final “launch commit” review. The goal is to ensure that all tasks associated with launch vehicle and satellite payload preparation have been completed, and that all assets needed to support the launch such as radar and tracking stations are available and working properly.
It’s also time for the satellite contractor team to go through its final checklist in preparation for launch.
“On the day of launch, we power up the satellite and configure it for launch,” explains Rob Woods, a satellite systems operation expert with Northrop Grumman. “If our technical team members spot anything they feel could jeopardize the safety or success of the mission, they can call for a launch hold or even a scrub.”
Skyway to Heaven
Following a nominal countdown and liftoff, the launch vehicle provider takes the lead during the early, or ascent, phase of launch. Teams on the ground monitor the health and status of the launch vehicle as its main stage and any booster stages execute their specified burns, then drop off. Once the launch vehicle reaches a predetermined altitude above the atmosphere, it also releases the payload fairing, exposing the satellite to the space environment.
During this ascent phase, the satellite contractor team puts the satellite into its separation configuration.
Satellite batteries only have so much power, so during launch and liftoff, only a minimum, critical set of hardware (typically command and data handling) is powered up,” says Woods. “Once a satellite separates from the second stage, however, it must be ready to assume complete control of itself, so all of its primary subsystems such as attitude control, propulsion, and communication have to be switched on.”
The second stage of the launch vehicle typically separates from the satellite and places it into either a circular low Earth orbit (LEO) or an intermediate transfer orbit. For more urgent, time-sensitive missions, the second stage might boost the satellite into a higher altitude (medium earth or geosynchronous) orbit before separation. Some satellites boost themselves from LEO to their final orbit using their own propulsion system, a process that can take several days, weeks or months.
Final Checks
Once the satellite reaches its final orbit, a team of engineers located at the satellite’s permanent ground control station — often located at a customer site — begins a disciplined, on-orbit checkout of the spacecraft. This team typically includes the satellite contractor and customer representatives.
“You can think of on-orbit checkout like the boot-up of your home computer, except that ours lasts for about 90 days,” explains Woods. “Unlike your computer, however, which was booted up many times before you purchased it, a satellite can’t be booted up in its operational configuration until the day you launch it. We have to turn things on very slowly and methodically.”
During this checkout phase, Woods continues, the ground operators configure the satellite for on-orbit operations. Their work includes powering on any remaining subsystems and mission payloads, and deploying the satellite’s solar arrays, communications antennae, payloads or other articulations.
“Once everything’s activated and deployed, we verify that all of our satellite subsystems are fully operational,” says Woods. “For example, we might change the pointing of the satellite, check that our star trackers are tracking stars as expected, or make sure that our mission sensors are seeing what they’re supposed to see.”
The team also calibrates the satellite’s instruments, and confirms, through a process called validation, that the data being collected by those instruments is consistent with expected and previously characterized data sets, he added.
The on-orbit check-out process typically takes 30 to 90 days depending on the size of the satellite and complexity of the mission.
Letting Go, Moving On
Before “turning over the keys” to the spacecraft, however, Woods and his team provide the satellite’s operators with all the critical and relevant details they’ll need to ensure the safe, continuous and effective operation of the spacecraft. After that, they are typically kept on stand-by to provide periodic maintenance support or to diagnose and help resolve any technical issues that arise once the satellite goes operational.
In summary, developing, producing and launching a satellite is a challenging, complex and extremely disciplined process. It takes the collective skills and talents of many people working toward a common goal. Space is a harsh and unforgiving environment, and critical details overlooked or misunderstood during satellite development can lead to disappointing or disastrous outcomes. If done right, however, every satellite has the potential to deliver valuable insights about the state of the planet and the human condition for many years to come.
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