Nicola Fox - Parker Solar Probe Project Scientist, Johns Hopkins Applied Physics Laboratory
Parker Solar Probe really is a historic mission, it was first dreamed of in 1958 and it has remained the highest priority mission throughout that period. The reason it hasn’t flown is just because it has taken a while for technology to catch up with the dreams that we had for this amazing mission.
The coolest thing about my job is just the sheer feeling that this is a 60-year journey that people have gone on to make Parker Solar Probe a reality and to be there at the finish line as we’re on the pad and ready to launch—that is definitely the coolest thing about my job.
After working on this for 10 years, it is really a pleasure to see it actually coming to fruition. To be one small part of this huge engineering team that is making science dreams come true is just amazing. I can’t wait to re-write textbooks and change the way we look at the Sun forever. I’m a whole ball of excited, and I honestly don’t know exactly how I’m going to feel at launch but I’m really excited to pass this off to the mission operations team and see all the science data that comes down and just get to enjoy all that Solar Probe brings us.
There are many enabling technologies, the solar arrays are really important, the autonomy is very important, one of the ones that is obviously also critical is the heat shield, and developing the technology to actually protect the probe at the Sun.
A sandwich panel is a lot like a honeycomb panel you find in a traditional spacecraft or on airplanes. You have the outer face sheets, and then you have a core. In this case the two outer face sheets are carbon-carbon composite, which is a lot like the graphite epoxy you might find in your golf clubs, it’s just been super-heated, and then the inside is a carbon foam. So the Parker Solar Probe heat shield has a white coating that’s on the Sun-facing surface of this giant frisbee that’s protecting the rest of the spacecraft. And that white coating was specially designed here at the lab, in collaboration with REDD and the space department as well as the Whiting school at Johns Hopkins proper, to actually work at the Sun, specifically designed for Solar Probe. And the concept is basically you’d rather be in a white car on a hot day, than a black car on a hot day—it just knocks down the heat that much more. So it’s helping us stay cool at the Sun.
The titanium truss was also specially designed for solar probe. It’s a really neat piece. It’s a welded titanium truss that’s about 4 feet tall, but it only weighs about 50 pounds. And the key there is we’re trying to minimize the conduction between the heat shield and the spacecraft, so you want to have as little stuff there as possible.
But then also the first closest approach will be a very interesting time. We’ll obviously be working towards closest approach a long time and getting science back from the beginning, but the heat shield has to do its hardest work 7 years into the mission, which has always been an interesting construct of the mission.
When we’re at closest approach, the front surface of the heat shield will be at about 2,500 degrees Fahrenheit. The back surface of the heat shield will be about 600 degrees Fahrenheit. But the spacecraft bus is basically sitting at 85 degrees Fahrenheit. So the shield is actually really keeping everything very cool, most of the stuff is on the bus.
The mission that is in its current form is actually a solar powered mission, whereas some of the earlier concepts were nuclear powered. So they just had different mission designs, there were different constraints on the mission, and so once this current form iteration with a flat heat shield, or 8-foot frisbee as we like to say, because it’s basically a giant sandwich panel protecting the spacecraft as an umbrella, really developed as a part of this solar-powered mission that is its most recent rendition. And so, reaching out with expertise all around the lab, that whole team really brought this heat shield to fruition.
Of all the space missions I’ve worked on, Parker Solar Probe is the most challenging and complex mission to design and to fly. The launch energy required to reach the Sun is 55 times that required to get to Mars, and two times to Pluto.
Annette Dolbow - Integration and Test Lead Engineer, Johns Hopkins Applied Physics Laboratory
So the tensest moment for me after launch is when we’re sitting in the control room and we’re waiting for that green telemetry to show that the spacecraft is turned on and we can actually talk to it.
Andy Driesman - Project Manager, Johns Hopkins Applied Physics Laboratory
The Parker Solar Probe is a technological marvel. The thermal protection system – the heat shield – will be glowing cherry red, the front surface of that will be 2500 degrees Fahrenheit, while the spacecraft will remain 85 degrees, roughly a warm day in Florida.
Parker Solar Probe needs electrical energy to operate, like any other satellite or most other satellites, the spacecraft has solar arrays, but unlike other satellites, we have to generate electricity very close to the Sun. For every watt of electrical energy we generate we have to dissipate 13 watts of thermal energy. To do that we need a cooling system. We have a cooling system that is much like you’d find in your car. There are two water pumps in the system that pump water through the solar arrays and up into radiators, those radiators radiate the energy to deep space, which is very cold, as opposed to a car where it would be radiated to air.
So Parker Solar Probe uses a sophisticated rule-based autonomy system to protect itself. For long periods of time the spacecraft can’t communicate to the Earth and it needs to take care of itself. So the engineers in the development phase spent a lot of time thinking about what faults could affect Parker Solar Probe, and came up with solutions to those faults. Those solutions are encoded in this rule-based autonomy system, so that even if there’s a fault on orbit—which of course we hope there isn’t—the system can take care of itself, and protect the spacecraft.
The real enabling technology was the heat thermal protection system. The material sciences just didn’t exist in the 60s and 70s, and so the carbon which came out of the military, looking for lightweight, stiff, strong structures, were the precursors to your tennis rackets and golf clubs, which are now the precursor to the carbon-carbon technologies that we have on Parker Solar Probe.
Ah, how do I feel. I feel excited, I feel a little bit scared. If we strap this thing, this spacecraft that we’ve been living with for almost a decade, we just strapped it to, we’re going to strap it to I don’t know how many thousands of pounds of hydrogen and oxygen and we’re going to put a match to it. And then, its going to take us into orbit, and from the time when we strike that match and the time where we hear from it again its about 43 minutes. That 43 minutes is the best, and the worst time, all combined into one. When that spacecraft comes over the horizon somewhere in Western Australia, or Eastern Africa and starts talking—the relief you feel is just unlike anything you’ve felt before. Because it’s alive—it’s warm, its in space where it was designed to be. Once you hear from it, and once the spacecraft is what we call power-positive – that means its generating more electricity that its using and can charge its batteries—once you’re able to talk to it, once its power positive, it’s…you know you’re good, you know you’re on your way. Because at that time, if there’s anything that goes wrong, you’ve got the power to do something about it.
One of the most common questions I get is “What happens if the spacecraft gets hit by a solar flare, or gets hit by a coronal mass ejection, will it be destroyed?”—that’s a very common question. And what I tell people is that the science community will be elated if we were to get hit by a solar flare or a coronal mass ejection. They’re very dramatic events when you look at them in the telescope or during an eclipse, but in the reality they’re very ethereal—the density of the particles isn’t so high to where it can actually cause damage to the spacecraft. But the instruments aboard the spacecraft—the electromagnetic field instruments, the high energy particles instruments, the plasma instruments, and the visible white light sensors, will see this event, and how dramatic would that be – to see a solar flare coming at you and fly right through it.
You design the instruments around the spacecraft, you design the spacecraft around the instruments, they’re all having to be designed to go through this horrendous environment.
Another reason Parker Solar Probe wasn’t launched in the last 60 years is that getting so close to the Sun is hard—it takes a huge amount of energy to get to where we want to go. When a satellite lifts off the Earth, it carries the Earth’s velocity around the solar system. The Earth is moving about 30 kilometers per second around the solar system. The spacecraft has to shed that energy in order to fall in to orbit around the Sun.
And if you look at the science data, there’s a big gap, and that gap is where Solar Probe is going. We’re going to fill that gap of scientific knowledge. So its true exploration in that, and we’re no following somebody – we’ll be the first spacecraft, the first people to go there. So what’ll be interesting is not the answers to the science questions, what’ll be interesting is the new questions that solar probe forces us to ask, because one thing we’re pretty sure of is that we probably have it somewhat wrong, and solar probe will teach us what’s right. And that will generate many more questions and many more missions to come.