4 ms·

> "Lauretta said there is nothing flight controllers can do to clear the obstructions and prevent more bits of Bennu from escaping, other than to get the sample

> "Lauretta said there is nothing flight controllers can do to clear the obstructions and prevent more bits of Bennu from escaping, other than to get the samples into their return capsule as soon as possible." This, I'm guessing. Also, I found these parts interesting: >"Regardless of what’s on board, Osiris-Rex will still leave the vicinity of the asteroid in March — that’s the earliest possible departure given the relative locations of Earth and Bennu. The samples won’t make it back until 2023, seven years after the spacecraft rocketed away from Cape Canaveral." >Because of the sudden turn of events, scientists won’t know how much the sample capsule holds until it’s back on Earth. They initially planned to spin the spacecraft to measure the contents, but that maneuver was canceled since it could spill even more debris. >“I think we’re going to have to wait until we get home to know precisely how much we have,” Lauretta told reporters. “As you can imagine, that’s hard. ... But the good news is we see a lot of material.”

rhn_mk1 6y ago
Thanks. That means there are two containers: the open one where the samples are now, and the sealed return capsule, where the contents will be transferred soon. In that light, this quote confuses me: > scientists won’t know how much the sample capsule holds until it’s back on Earth. They wanted to spin the spacecraft to measure the mass, but they can't risk losing more samples from an open container. But why can't they spin the spacecraft after the sample is secure in the return capsule, but before reaching Earth? Is it precisely in the center of mass?
- SamBorick 6y ago
  I recommend the scott manly video another commenter linked to for a more full explanation, but: The sample container that's currently jammed open is on the end of a long arm, while the sample return capsule is mounted on the body of the spacecraft. The only way to measure mass in free-fall is to spin the entire craft and measure where the center of rotation is compered to before the sample capture. The difference is then used to calculate the sample mass. With the sample at the end of a long arm, the spacecraft doesn't have to rotate very fast to get a large enough difference in rotation to measure the sample. If the sample is in the return capsule, the moment is so much smaller that it's probably below the sensitivity of the instruments they were planning to use.
  - yetihehe 6y ago
    Bright side - they have so much material, that weighting it is not really that much of a concern. They were hopeful to get maybe 50 grams of material, they got about 400g, but maybe 100g will be lost. They won't have exact number, but they will have more than expected anyway.
    - Jaruzel 6y ago
      Won't the extra weight require a change in earth re-entry fuel calculation etc. ? Without knowing the exact change in weight, they are going to be firing in the dark, as it were.
      - yetihehe 6y ago
        I don't know that much, but I suppose they will do a burn and then some corrections. If mass difference is big enough to be detectable for reentry, it will be detectable when they are going back to earth.
        LeifCarrotson 6y ago
        A key difference is that spinning the full satellite with the arm extended and measuring the center of rotation measures the mass of the samples collected regardless of the thrusters/reaction wheels. Measuring the trajectory of the reentry vehicle gives a parameter that can be used to estimate the sample mass assuming nominal thrust values, but you can't distinguish between an underperforming or overperforming rocket engine and heavier or lighter samples. This ambiguity doesn't really matter for the purposes of burn correction - you need to get to the correct reentry trajectory no matter what caused the deviation - but your sample mass estimate may be off. I don't think there's a whole lot of utility in knowing the sample mass, as long as you've got enough (and they've definitely got enough!), it would just help satiate the curiosity of the scientists and engineers who otherwise have to wait a few more years to see their results.
      - awalton 6y ago
        It's not enough to make a difference either way around it. The sample return container could be filled to the brim with pure osmium or iridium and would make it through the atmosphere just fine. The scientists are mostly worried because they want as much of the sample as they can possibly get, and they're a little worried about closing the sample container - if there's a rock that gets stuck somewhere, the container might not seal shut and then they've got a real bad problem they've gotta contend with. It's 2020, they don't want to jinx it, just shut it up in the container and wait for the time capsule to arrive in 2023.
- rtkwe 6y ago
  The sample return vehicle is much closer to the center of the vehicle so the change in the moment of inertia will be much smaller than if they had been able to extend the arm as planned. The change would be pretty slight and maybe on the edge of what is meaningfully measurable.
- bitcurious 6y ago
  > But why can't they spin the spacecraft after the sample is secure in the return capsule, but before reaching Earth? Is it precisely in the center of mass? They might be able to, but there’s no reason to. The purpose of the sample mass measurement was to determine if they needed to try again, however that’s not an option with a jammed container.
  - duskwuff 6y ago
    And the criterion for trying again is that they didn't collect enough material on the first try. If there's so much sample in the container that it's jammed open, they're probably fine in that regard. :)

rhn_mk1 6y ago

Thanks. That means there are two containers: the open one where the samples are now, and the sealed return capsule, where the contents will be transferred soon. In that light, this quote confuses me: > scientists won’t know how much the sample capsule holds until it’s back on Earth. They wanted to spin the spacecraft to measure the mass, but they can't risk losing more samples from an open container. But why can't they spin the spacecraft after the sample is secure in the return capsule, but before reaching Earth? Is it precisely in the center of mass?

SamBorick 6y ago
I recommend the scott manly video another commenter linked to for a more full explanation, but: The sample container that's currently jammed open is on the end of a long arm, while the sample return capsule is mounted on the body of the spacecraft. The only way to measure mass in free-fall is to spin the entire craft and measure where the center of rotation is compered to before the sample capture. The difference is then used to calculate the sample mass. With the sample at the end of a long arm, the spacecraft doesn't have to rotate very fast to get a large enough difference in rotation to measure the sample. If the sample is in the return capsule, the moment is so much smaller that it's probably below the sensitivity of the instruments they were planning to use.
- yetihehe 6y ago
  Bright side - they have so much material, that weighting it is not really that much of a concern. They were hopeful to get maybe 50 grams of material, they got about 400g, but maybe 100g will be lost. They won't have exact number, but they will have more than expected anyway.
  - Jaruzel 6y ago
    Won't the extra weight require a change in earth re-entry fuel calculation etc. ? Without knowing the exact change in weight, they are going to be firing in the dark, as it were.
    - yetihehe 6y ago
      I don't know that much, but I suppose they will do a burn and then some corrections. If mass difference is big enough to be detectable for reentry, it will be detectable when they are going back to earth.
      - LeifCarrotson 6y ago
        A key difference is that spinning the full satellite with the arm extended and measuring the center of rotation measures the mass of the samples collected regardless of the thrusters/reaction wheels. Measuring the trajectory of the reentry vehicle gives a parameter that can be used to estimate the sample mass assuming nominal thrust values, but you can't distinguish between an underperforming or overperforming rocket engine and heavier or lighter samples. This ambiguity doesn't really matter for the purposes of burn correction - you need to get to the correct reentry trajectory no matter what caused the deviation - but your sample mass estimate may be off. I don't think there's a whole lot of utility in knowing the sample mass, as long as you've got enough (and they've definitely got enough!), it would just help satiate the curiosity of the scientists and engineers who otherwise have to wait a few more years to see their results.
    - awalton 6y ago
      It's not enough to make a difference either way around it. The sample return container could be filled to the brim with pure osmium or iridium and would make it through the atmosphere just fine. The scientists are mostly worried because they want as much of the sample as they can possibly get, and they're a little worried about closing the sample container - if there's a rock that gets stuck somewhere, the container might not seal shut and then they've got a real bad problem they've gotta contend with. It's 2020, they don't want to jinx it, just shut it up in the container and wait for the time capsule to arrive in 2023.
rtkwe 6y ago
The sample return vehicle is much closer to the center of the vehicle so the change in the moment of inertia will be much smaller than if they had been able to extend the arm as planned. The change would be pretty slight and maybe on the edge of what is meaningfully measurable.
bitcurious 6y ago
> But why can't they spin the spacecraft after the sample is secure in the return capsule, but before reaching Earth? Is it precisely in the center of mass? They might be able to, but there’s no reason to. The purpose of the sample mass measurement was to determine if they needed to try again, however that’s not an option with a jammed container.
- duskwuff 6y ago
  And the criterion for trying again is that they didn't collect enough material on the first try. If there's so much sample in the container that it's jammed open, they're probably fine in that regard. :)