Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
Readers’ wildlife will be postponed until tomorrow so that we can see astronomical “wildlife.”
Once again our faithful space-exploration reporter, Jim “Bat” Batterson, found some new photos of the DART impact on the asteroid Dimorphos, an attempt to knock the small asteroid out of its normal orbit around its larger companion asteroid, Didymos. This was, of course, a practice to see if we could perturb the course of a future celestial body that actually might hit the Earth. The impact was on target, but we don’t yet know whether we perturbed its orbit in the expected way.
Here’s a photo from Wikipedia of Dimorphos taken from the DART spacecraft moments before impact. It’s a pile of rubble! The diameter is 170 meters, or 560 feet.
The rubble really blasted out! Because of small gravitational field of the impacted asteroid, I imagine that some of the debris may form a ring around the larger one, some might have escape velocity from the system itself and just continue in orbit around the sun, and of course some may slowly drift down back onto Dimorphos’ surface. I hope that the engineers will hold a press conference about this and I hope that they got a picture of the impact point and crater.
But I’ll show you the NASA pictures below. They were taken by DART’s companion spacecraft, the LICIACube (from “Light Italian CubeSat for Imaging of Asteroids”), the first autonomous spacecraft developed by a wholly Italian team under the Italian space agency. It was a tiny minicraft affixed to DART with the express purpose of photographing the impact. As the Wikipedia note shows below, it separate from DART more than two weeks before impact:
After the launch, the Cubesat remained enclosed within a spring-loaded box and piggybacks with the DART spacecraft for almost the entire duration of DART’s mission. It separated on 11 September, 2022 from DART by being ejected at roughly 4 km/h (2.5 mph) relative to DART, 15 days before impact. After release, as part of the testing process to calibrate the miniature spacecraft and its cameras, LICIACube captured images of a crescent Earth and the Pleiades star cluster, also known as the Seven Sisters.
It conducted 3 orbital maneuvers for its final trajectory, which flew it past Dimorphos about 2 minutes 45 seconds after DART’s impact. That slight delay will allow LICIACube to confirm impact, observe the plume’s evolution, potentially capture images of the newly formed impact crater, and view the opposite hemisphere of Dimorphos that DART will never see, while drifting past the asteroid.
Here’s the LICIACube by itself and then affixed to the DART spacecraft (I’ve circled it in the second photo). Look how small they can make a satellite these days!
As Jim wrote:
The LICACub is about 4x8x12 inches. The cube class of vehicle (cheaper) was initiated by NASA in the 90’s, if I recall correctly, to give access to a broader class of potential users who wanted to conduct Their own space experiment.
The full DART mission itself is one of another class of “cheaper” at $300M or so compared with the more than $1B major mission to Pluto and beyond.
And the pictures that the cube took from NASA, with their captions (click to enlarge). They all show the dust cloud around Dimorphos after the impact:
Image captured by the Italian Space Agency’s LICIACube a few minutes after the intentional collision of NASA’s Double Asteroid Redirection Test (DART) mission with its target asteroid, Dimorphos, captured on Sept. 26, 2022. Credits: ASI/NASA
Image captured by the Italian Space Agency’s LICIACube a few minutes after the intentional collision of NASA’s Double Asteroid Redirection Test (DART) mission with its target asteroid, Dimorphos, captured on Sept. 26, 2022. Credits: ASI/NASA
Image captured by the Italian Space Agency’s LICIACube a few minutes after the intentional collision of NASA’s Double Asteroid Redirection Test (DART) mission with its target asteroid, Dimorphos, captured on Sept. 26, 2022. Credits: ASI/NASA
Here, from Facebook, is a lovely video taken from a telescope on Earth showing the impact. The asteroid system, in the center of the screen is moving to the left relative to the stars in the background:
There are a few more videos and more information in this article from the NYT (click to read):
Two days ago, Jim Batterson, an old friend and college classmate who worked for NASA for many years, wrote a precis of the DART mission designed to knock a small asteroid out of its orbit around a bigger asteroid. He and I were two of the many who watched the “near live” impact of the spacecraft on Dimorphos, and we were both thrilled. Here’s the last 18 seconds before impact:
Here, from Facebook, is a telescopic view from Earth of the moment the spacecraft hit Dimorphos (credit: Atlas Project):
After I mentioned to Jim that this was the first time we tried to perturb an orbit with a spacecraft, he sent me his thoughts on the mission and reminded me of a few instances of other impacts or landings on celestial bodies, though these didn’t have the same goal as DART. With his permission I submit Jim’s thoughts for your approval.
Some Post-DART Mission Thoughts
Jim Batterson
Now that the excitement and really spectacular success of the DART asteroid rendezvous and impact is in the rearview mirror, I want to remind readers of some earlier space missions that were akin to DART in an engineering sense.
Much of what NASA does in space missions is “engineering in the service of science”. That is, NASA scientist and engineers, in consultation with scientists from around the world, are responsible for managing and assuring the design of appropriate missions, building (often unique) scientific instruments, and developing the rockets and spacecraft to fly those instruments to a point in space (sometimes on a planet or simply in a planetary atmosphere) where collected data is returned for analysis to scientists on Earth. Comet rendezvous missions are traditionally “pure science” missions to gather unique data on the composition of comets, as it’s thought that a better understanding of comets will lead to a better understanding the formation and early years of our solar system.
DART was a different type of mission, not only in its focus on an asteroid rather than a comet, but also in that it kept its engineering mission for planetary defense pretty clean and did not try to add in a large suite of scientific instruments to gather data. That said, there have been several comet flybys over years and two comet impacts
The impacts were these:
Deep Impact by NASA/Jet Propulsion Lab (JPL). Upon rendezvousing with the Comet Temple-1 on July 4, 2005, the Deep Impact spacecraft launched an impactor craft that smashed into the comet’s nucleus. The debris cloud and crater were then photographed and analyzed by instruments on the mother ship. Here’s a NASA photo with this caption:
This spectacular image of comet Tempel 1 was taken 67 seconds after it obliterated Deep Impact’s impactor spacecraft. The image was taken by the high-resolution camera on the mission’s flyby craft. Scattered light from the collision saturated the camera’s detector, creating the bright splash seen here. Linear spokes of light radiate away from the impact site, while reflected sunlight illuminates most of the comet surface. The image reveals topographic features, including ridges, scalloped edges and possibly impact craters formed long ago.
Source: NASA/JPL-Caltech/UMD
The Rosetta/Philae mission was carried out by the European Space Agency (ESA) in 2014. Upon rendezvous with Comet 67P after an almost eleven-year journey through space, the Rosetta spacecraft launched a lander (Philae) whose purpose was to soft-land on the comet and drill into its surface, gathering data on the comet’s interior. ESA was partly successful as Philae did make it to the surface. But some of its propulsion equipment failed to operate properly to slow it down completely, so it suffered a hard landing and bounced, leaving Philae in a crevice. This prevented it from accessing sunlight needed to recharge its batteries. Sadly, the subsurface data couldn’t be collected.
However, it did survive to take some incredible photos on the actual surface of a comet nucleus. I think that this was still an extraordinary accomplishment. You can see the photos here.
[JAC: I’ll present one example, a fantastic selfie taken by Philae as it sat in the crevice. The caption is
“The Philae lander of the European Space Agency’s Rosetta mission is safely on the surface of Comet 67P/Churyumov-Gerasimenko, as these first two images from the lander’s CIVA camera confirm. One of the lander’s three feet can be seen in the foreground. The view is a two-image mosaic taken on Nov. 12, 2014.”]
DART didn’t even pretend to be about collecting basic science data, but rather was about using engineering expertise developed over our spacefaring years to help the protect our planet. This was an important proof of a “concept mission” in which the concept was that, if an asteroid were given a proper nudge, its trajectory could be changed enough to move it from a collision course with Earth to a harmless close encounter. This was a test or experiment to gather engineering data. It is a high-school physics problem to show that it works in theory, but would it work in the real world?
I think that one of big engineering challenges for the DART test was navigating and guiding using the light from the two-asteroid system and then, a few minutes before scheduled impact, to autonomously focus on and keep the smaller, dimmer asteroid as its target. This was especially challenging because the engineers had no real knowledge of the reflective characteristics or shape of either body. It turned out, as we all saw in the final couple of minutes of approach, that both bodies were non-spherical with lots of surface irregularities, which scatter sunlight in all directions and cast shadows. But the software had been designed with enough robustness to deal with these non-ideal bodies.
For folks who want to learn more about Near-Earth Objects, I recommend Donald Yeomans’ 2013 book, Near-Earth Objects: FindingThem Before They Find Us (Princeton) as an excellent summary the general reader.
. . . well, the spacecraft hit the asteroid perfectly—couldn’t have been better. It was lovely to see it in real time, with Dimorphos getting bigger and bigger as DART hurtled towards it at 14,000 mph. It’s the first time our species has tried to alter the motion of an extraterrestrial body.
Well, I’m gobsmacked. Here’s a screenshot I took of Dimorphos about 2 seconds before the spacecraft hit it.
Note: because I have several items to bring to your attention, the “readers’ wildlife post” will be suspended for today, but will resume tomorrow.
Today—to be precise, at 7:14 p.m. EDT (6:15 Chicago time)—is the day that the DART mission (Double Asteroid Redirection Test) culminates in a NASA spacecraft, launched last November, crashing into a small asteroid in orbit around a longer one. The goal, as my friend Jim Batterson writes below, is to see if humans even have the ability to deflect an asteroid, comet, or any smallish body heading for a collision course with Earth. (This asteroid isn’t on a collision course; this is just a test.) If you want to see the upshot, I recommend going online at least fifteen minutes at the time given above. (Actually, you should be able to see a small image of the asteroids an hour before the crash.) The the news of the mission’s success or failure will take about 45 seconds to reach the earth, as the signal must travel 7 million miles at the speed of light. The link you want to watch is at the bottom as an embedded YouTube video.
I am absolutely amazed that we can even try to do this, especially because the collision is guided automatically rather than manually (see below) and was calculated precisely using Newtonian physics. And note the asymmetry of the collision: as the Associated Press reported:
“This really is about asteroid deflection, not disruption,” said Nancy Chabot, a planetary scientist and mission team leader at Johns Hopkins University’s Applied Physics Laboratory, which is managing the effort. “This isn’t going to blow up the asteroid. It isn’t going to put it into lots of pieces.” Rather, the impact will dig out a crater tens of yards (meters) in size and hurl some 2 million pounds (1 million kilograms) of rocks and dirt into space.
The size of a small vending machine at 1,260 pounds (570 kilograms), the spacecraft will slam into roughly 11 billion pounds (5 billion kilograms) of asteroid. “Sometimes we describe it as running a golf cart into a Great Pyramid,” said Chabot.
Jim “Bat” Batterson is an old college friend who worked for NASA for many years and has kept me informed about the DART mission. He kindly offered to summarize the mission for me, and the indented bit below is what he wrote. Thanks, Bat!
Asteroid Impact Test Mission September 26, 2022 (Impact at 7:14 PM)
Jim Batterson
The DART (Double Asteroid Redirection Test) is scheduled to be completed today, September 26, 2022, at 7:14 PM EDT. DART is an international space mission led by NASA and the Johns Hopkins Applied Physics Laboratory. Its mission is carry out the first in situ test of the theory that an asteroid on a collision course with the Earth can be deflected by the momentum of an impacting spacecraft into a new trajectory that will miss Earth.
This test involves spacecraft hitting a near-Earth asteroid that is NOT on a collision path with Earth. The impacting spacecraft has been journeying toward the double asteroid system, Didymos and its moonlet Dimorphos, since its November 2021 launch from Vandenberg AFB in California. The target, Dimorphus, the smaller of the two asteroids, is about 500 feet across. The impact will occur approximately 7 million miles from Earth, so pictures and data should be available in near real-time. A smaller companion spacecraft is programmed to miss the asteroid and and to try to photograph the impact.
The path over the past 10 months to a rendezvous millions of miles from Earth has involved yet another extraordinary engineering effort to guide a spacecraft through the perturbing effects of gravity from planets and the varying solar wind in the otherwise benign vacuum of space.
NASA has been following Near-Earth Objects in space for many years to prepare for any genuine predicted impact and to ensure that humans in space are not threatened by these objects. Part of the NASA research program has also included determining whether redirecting a certain size-class of objects that might be on an Earth-intersecting trajectory—and which could cause catastrophic harm if they were to impact Earth—by hitting the object with a spacecraft while the object is still far away from Earth. The large distance allows a small change in trajectory of the target to result in missing Earth by a wide shot.
While mathematical models and simulations have been very encouraging over the years, DART is the first actual in situ physical test of the theory. The theory is just simple Newtonian mechanics—much like the strategy of billiards in which a ball is hit into another ball and both balls change speed and direction. But in the DART experiment, one ball, the asteroid, is 8 million times more massive than the other. This is much like trying to change the trajectory of a bowling ball by impacting it with a grain of sand. Because the amount of change in direction depends on not just the masses, but rather on the momentum (the product of mass times velocity), the smaller object (the spacecraft) must be moving very fast to impart any significant momentum to the asteroid. That will be the case tonight as the refrigerator size, 1000 lb. craft will crash into the asteroid at ~15,000 MPH!
The last human input guiding the spacecraft will occur about four hours before scheduled impact. That’s when when the image of the asteroid gets centered in the field of the craft’s onboard digital camera by ground controllers using hydrazine thrusters for orientation. Because the craft is closing in on the asteroid at about 4 miles per second, and it takes the better part of a minute for a round trip of a radio signal between Earth and the spacecraft, from that point on the DART craft maneuvers totally autonomously using its hydrazine thrusters to keep the target image centered in the camera’s field of view.. We should see pictures taken from that camera during descent as well from a companion spacecraft designed photograph the impact and any post-impact disturbances at and above the surface of the asteroid.
I don’t know if these raw data images will be made available to the public in near real time or only after some image processing. Any resulting momentum change will be detected by a change in orbit characteristics for the twin asteroid system as calculated from Earth-based observations.
The latest information I have (as of September 25) is that impact should occur at 7:14 PM EDT on Monday, September 26. The mission is scheduled to be covered live on NASA TV starting at 6:00 PM EDT. Go to NASA TV at https://www.nasa.gov/nasalive, or just click below [JAC: check the news in case there is any change in time, though I don’t expect one.]
WATCH HERE:
You can see pretty complete background information at scitech.
Finally, Jim wanted me to give this caveat about what he said, and adds that he welcomes any corrections:
I think this is pretty close to being correct, but I was more of an airplane/spaceplane guy – not an orbital or outer-space guy. So You might add the caveat that this is from my study of publicly available mission documents, back of the envelope calculations, and general accumulated knowledge of NASA missions in general from a thirty-year career that ended in 2008. Without peer review I cannot attest to total accuracy, but as you say: I try my best.
The expected perturbation of Dimorphos’s orbit. Note the accompanying LICA Cube that will photograph the impact (if it occurs). If there’s no impact, there will be a second chance later as the DART craft returns. The AP notes that “Little Dimorphos completes a lap around big Didymos every 11 hours and 55 minutes. The impact by Dart should shave about 10 minutes off that.”
Here’s a four-minute video about the mission and how scientists will watch the impact and measure its effect:
Finally, a short AP film that starts with November’s launch:
In lieu of readers’ wildlife today (the tank is quite low), and because we pay attention to space exploration, take note that the rescheduled Artemis-1 mission is scheduled for this afternoon. That doesn’t mean it will take off, but it means they’ll try.
My friend James “Bat” Batterson, a now-retired physicist who worked for NASA, has patiently answered my inquiries about the Artemis mission, the mechanics of rockets, and so on. So I asked him to write a bit about the launch, which is below. You can watch it from the NASA site, though I prefer Space.com, which you can watch right here. Tune in about 2 pm Eastern time.
After reviewing sensor data and a full physical inspection of the Artemis-1 Space Launch System (SLS) rocket and components, NASA has rescheduled this past Monday’s canceled test flight. The new proposed launch of of this un-crewed vehicle occupies a two-hour window that begins at 2:17 EDT this afternoon.
In a nutshell, after looking at redundant data from other sensors and their experience base, the managers believe that a temperature-sensor reading —one that told them that one of the rocket engines had not cooled to a proper temperature of approximately -420F for launch (it was reading -370F)—was wrong. They’ve also fixed a coupling that leaked on Monday and decided that an insulation crack on the main cryogenic fuel tank did not pose a danger.
Followers of the Shuttle program may recall that a piece of foam insulation that tore loose from Shuttle Columbia’s fuel tank on launch and impacted the Shuttle wing causing a large hole that allowed hot gas into the wing during re-entry into the Earth’s atmosphere a week later. That, of course, led to destruction of Columbia and the loss of all astronauts onboard. The SLS is a safer design with the crew module configured above the tank.
While not as tall as the Saturn-5 that powered Apollo astronauts to the Moon, this rocket is more powerful, allowing for a significantly heavier payload to be delivered into lunar orbit. Its main stage propulsion system uses four RS-25 Space Shuttle engines (the shuttle used three), in tandem with two solid rocket booster engines. Together these provide over eight million pounds of thrust. The solid boosters last for two minutes before being jettisoned. As with the shuttles, the boosters then fall into the Atlantic. The four RS-25’s burn for eight minutes, putting the payload into a 17,500mph low-Earth orbit.
Later, a second-stage rocket burn will accelerate the payload to more than 22,000 mph to send it into a lunar trajectory, a trip that takes several days. [The orbiting of the Moon begins September 8, with the module coming back to Earth on October 11.] CBS News has an excellent write-up here. If you want to know more about the mission details and the ultimate goal of getting people to live on the Moon, go to the Astronomy article here.
And an important note:
This is an engineering test flight, not a demonstration flight. They have tested all the parts in isolation and in partial configurations, but this is a test of the whole system designed to carry out a mission to the Moon and back, ending with a safe splashdown. As I emphasized last week, a whole lot of things need to go extraordinarily right, and those that don’t have been designed in what is known as a “fail/operate” mode* so that the entire vehicle and thus the mission does not fail.
Here’s the best place to watch it: the NASA live site at space.com:
* “Fail/safe” refers to the eponymous book and movie on nuclear war. It refers to a design that, if the booster rocket were to fail, the crew would be rocketed away in their own capsule and splash down safely. The space shuttles obviously were not designed that way, but the space launch system is.
Here’s a diagram of the planned itinerary (from the Astronomy article), with the outbound leg in green and the return leg in blue. Click to enlarge:
UPDATE: Today’s launch has been scrubbed because there’s a problem with the cryogenic hydrogen that’s used as fuel. They are still troubleshooting as they have no idea what’s wrong. The earliest that a launch can occur is now early afternoon Friday, so stay tuned.
________________________
I’m putting this up early as the blastoff could occur as early as 8:30 Eastern time. The announcement was sent to me by my William & Mary pal James “Bat” Batterson, who used to work for NASA, and I’m putting it up exactly as he sent it (indented):
Just a heads up that first moonshot with human-capable Orion spacecraft is scheduled for Monday morning in a window between approximately 0830 and 1030 EDT from Cape Kennedy. This rocket is as powerful as the Saturn V of the Apollo days of the 1960’s and 70’s and should be an impressive (noisy) blast off. As best I can tell – I have not followed things that closely – the first 8-9 minutes, as with the space shuttles, is the critical period to low earth orbit (LEO), with the next several hours having scheduled boost burns to get the vehicle into a lunar trajectory for the next several days.
This will be an uncrewed rehearsal, but will cycle through all stages required for a human-crewed flight to the Moon. So fingers crossed that it will be successful. As with anything this complex, lots of things need to go extraordinarily right.
There appears to be lots of streaming and tv coverage planned including CNN; i expect even the networks but they will likely have obnoxious talking heads; and my usual go-to: space.com which usually links in NASA TV live.
Here’s the live NASA feed. As I watched this at about 5 a.m. Chicago time, there was already a hydrogen leak that they were trying to repair.
An update from Bat at 6:30 Eastern time:
I am watching on space.com which has a video of nasa.live going. Came on air at 0630. There are some issues being worked with fuel and they think that the planned 0832 launch time may slip but do not know by how much yet. There are really crisp beautiful views of the full rocket and of some of its components. One of the great technological advances since apollo has been digital video in place of film!
You will notice that the configuration has the capsule that will carry people in future missions at the top of the stack, ahead of the rocket fuel. This is due in a large part from a safety lesson taken from space shuttle flights that it is dangerous to have people positioned next to fuel as it makes an emergency abort difficult to impossible. This system has a launch abort system (LAS) that, in case of an emergency, can engage and quickly carry the capsule well away from the booster anytime from sitting on the launch pad and into the first few minutes of flight. One of my former engineers is flight dynamics lead on the LAS, a project he started working on about the time that I retired in 2008. These very complex engineering projects do not happen overnight!
NBC in the Bay Area has a photographic as well as a data comparison of both the crew modules and booster rockets. For example, here’s the Apollo module that was part of the Moon launches:
The toughest bit, though seems past: successfully unfolding the entire mirror of the Webb Space Telescope was the most delicate of all its operations, since nothing could fail without endangering the scope’s usefulness. And nothing did! NASA has reported, along with many other sites, that the main mirror deployment is, as they say, “nominal.” From Space.com:
JWST’s golden primary mirror includes 18 individual hexagonal segments, each controlled by seven actuators that allow precise movements. All 18 segments are now in their deployed positions several days sooner than scheduled.
Work began on the mirror segments on Jan. 12 and was expected to take about 10 days. But despite today’s announcement, those mirror segments aren’t quite ready to observe yet. First, NASA must conduct the painstaking process of fine-tuning every mirror’s position to turn 18 individual views of the universe into one large ultra-powerful mirror.
The team behind Webb expects that the entire mirror process will take about three months, all told.
Here’s a NASA video of the immensely complicated process of aligning all the mirrors once they’ve unfolded. I have faith in the Telescope Humans that all will be well.
More:
If this works okay, and nothing else goes wrong, in a few months the scope will be in position and ready to send data. There is one more important maneuver:
Webb has one more key deployment milestone to complete, a trajectory burn that will insert the observatory into orbit around a spot in space dubbed the Earth-sun Lagrange point 2, or L2. L2 is located nearly 1 million miles (1.5 million kilometers) away from Earth, on the side of the planet opposite the sun.
According to a NASA timeline, JWST is expected to complete this final arrival maneuver on Sunday (Jan. 23).
A good site to follow is “Where is Webb?” NASA’s real-time timeline of the mission showing the location of the scope and what it’s doing. Below is a screenshot that you can click on to see where Webb is now. It’s approaching “L2 insertion” on the right! Click on the photo to enlarge it.
