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as we started to approach bennu from a

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distance and it started to fill up the

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camera field of view it looked exactly

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like we thought it would with a few

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boulders sticking out but as we got

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closer we expected to see a very sandy

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surface with maybe a few boulders here

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and there and what we saw is

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very little sand and we saw these

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mountains we saw boulders we saw rocks

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and we saw very few areas that had this

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sandy surface that we were expecting and

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we have never done this before

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we're actually going to collect a sample

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and bring it back down to earth for

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further examination by

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scientists in order to achieve that

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objective the osiris-rex spacecraft has

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been navigating around bennu for about

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the last two years studying it in great

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detail and also overcoming a number of

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challenges that bennu has presented we

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were looking for locations on venue that

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were 50 meters in diameter relatively

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flat and covered with fine-grained

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material and by fine-grained material i

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mean stuff that's the size of a dime or

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smaller we realized that there were no

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sites on bennu that even came close to

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meeting this criteria everywhere we

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looked was too small and covered with

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boulders so we actually had to fly a

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number of additional close passes over

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the asteroid and rethink our entire plan

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after the additional observations of

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bennu we had to down select to four

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sites and then go back and survey those

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sites even further to select the final

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primary sample site my first impression

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of nightingale is that's the last place

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i wanted to go but as we started looking

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at other sites we saw that one this is

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probably one of the most sampleable

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sites and two we were over performing in

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our navigation capability and our

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ability to contact

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natural feature tracking works a lot

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like the human mind in that we pick up

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landmarks along the way as we descend we

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look at features on the ground we

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program the computer to recognize

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certain features it takes a picture says

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this feature is not where i expected it

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to be it's a little bit off to the side

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updates its position based on where it's

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pointed and where that feature shows up

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in the camera position

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the tag event is our touch and go event

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which is where we'll actually be

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retrieving the sample from asteroid

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bennu we start with a series of

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maneuvers one of them being the

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checkpoint burn which is where we'll

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actually check our position velocity in

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relation to the sample sites and then

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the match point burn about 10 minutes

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later we'll zero out our horizontal

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velocity relative to the surface and

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then about 10 minutes after that we make

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contact with the tag sam fire the gas

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bottle and then back away and we hope to

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get at least 60 grams of sample and then

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we'll be able to store that and bring it

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back down to earth but there are several

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things that could go wrong and we also

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have to be prepared that we won't be

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successful on our first try at

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nightingale

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we don't only get one shot at tag we

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actually have three nitrogen bottles on

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board the spacecraft so we can

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potentially do three tag attempts if

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needed we go through several what-if

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scenarios and this is how we actually

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prepare for a lot of our contingencies

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so we've had to look all around the

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surface and identify the rocks and

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boulders that if the spacecraft were to

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tip over up to 25 degrees

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it could come into contact and be

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damaged we had to develop a hazard map

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which we program into the computer and

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says if you're getting too close to

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those hazards we'll do a wave off we'll

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back away from the asteroid we'll come

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back and do this another day everything

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might work perfectly we come down we

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touch the surface just where we want to

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we fire the gas bottle but the area we

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contact is covered in large rocks

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those rocks would prevent any fine grain

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material from being stirred up and

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captured in the tag sam head

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another similar scenario is if the tag

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sam were to touch on the edge of a

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boulder and become tipped up in that

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case when the gas bottle fires much of

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that gas escapes out the side not

109
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churning up the material that we want to

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capture the day of tag is going to be

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really exciting but the excitement for

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our team doesn't end there we have to

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verify that we have a proper sample

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first we're going to image the tag sam

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head by sticking in front of one of the

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cameras then we're going to do a

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maneuver called the sample mass

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measurement in which we stick out the

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arm and we spin the spacecraft in order

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for us to decide if we've collected

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enough mass to be able to stow the

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sample and return home or if we have to

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try again this is the culmination of a

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lot of work it's probably one of the

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most exciting missions that i've worked

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on it is really exciting to know that

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we're finally going to be able to

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touch the surface of the asteroid and

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collect the sample to return back to