tag:blogger.com,1999:blog-3596550435682943926.post827993711511317373..comments2024-03-29T03:35:30.962-07:00Comments on Hop's Blog: Making the tether catchHop Davidhttp://www.blogger.com/profile/12923433894475072056noreply@blogger.comBlogger10125tag:blogger.com,1999:blog-3596550435682943926.post-74680239779036754742015-10-28T16:21:58.370-07:002015-10-28T16:21:58.370-07:00The cartoons imply the spacecraft is approaching t...The cartoons imply the spacecraft is approaching the catcher horizontally. But it looks to me like the spacecraft is approaching vertically, parallel to the length of the tether. That being the case, a funnel on the end of the tether seems a better representation of the catcher. The natural path of approach is through the floor of the landing platform illustrated.hanelyphttps://www.blogger.com/profile/07173046002862833762noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-32145969355572571762015-07-23T16:30:03.459-07:002015-07-23T16:30:03.459-07:00For ships coming in from an interplanetary trip, I...For ships coming in from an interplanetary trip, I would be inclined to use the ships ion drive to put it in a highly elliptical orbit that rendevous with the outer tip of the Phobos or Deimos tether. That way a missed catch can be recovered days later.Jim Baergnoreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-81565971556416393332015-07-09T08:46:40.008-07:002015-07-09T08:46:40.008-07:00Doug, the video is of a rotavator in earth orbit. ...Doug, the video is of a rotavator in earth orbit. I linked to it because it shows a mechanism for making fast paced catches.<br /><br />The Phobos and Deimos elevators would be vertical tethers. For these timing is much less of an issue than with rotavators. <br /><br />When a tether rendezvous point is more distant from the balance point, net acceleration is greater. It is the net acceleration that sets the pace of the catch. A Phobos tether foot just above Mars' surface would feel the highest net acceleration, about .3 g. This is the only rendezvous point where the pace of the catch is comparable to what's show at 3:10 of the <a href="https://www.youtube.com/watch?v=mPx1Nq80jm8" rel="nofollow">rotavator video</a>.<br /><br />If a ship launched from Mars surface misses the tether foot, it could land downrange of the launch site.Hop Davidhttps://www.blogger.com/profile/12923433894475072056noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-33193976274600219842015-07-07T16:54:36.924-07:002015-07-07T16:54:36.924-07:00So, the video shows precious little time to make t...So, the video shows precious little time to make the catch and it assumes that the vehicle and the rotation of the tether matches very closely. In the video, if the capture had been missed, how likely would it be that the situation would be redeemed later?DougSpacehttps://www.blogger.com/profile/03057371106251356495noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-8754993870512218742015-07-04T12:37:45.944-07:002015-07-04T12:37:45.944-07:00Magico, you're right about the suborbital catc...Magico, you're right about the suborbital catch to Phobos tether foot. It's way faster and feeling a healthy acceleration. I'm not even sure a landing platforum would be appropriate, but whatever the catching mechanism it should be mobile.<br /><br />Maybe something along the lines of this video at 3:20 : https://www.youtube.com/watch?v=mPx1Nq80jm8Hop Davidhttps://www.blogger.com/profile/12923433894475072056noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-77193742126501428192015-07-04T10:32:41.501-07:002015-07-04T10:32:41.501-07:00Sorry, I was thinking ahead to the Mars suborbital...Sorry, I was thinking ahead to the Mars suborbital to Phobos-tether bottom transfer, where the elliptical orbit will be tighter and less forgiving of any rendezvous mistiming or plain old miss.<br /><br />Any vehicle ought to be able to use thrusters for adjustment, it's true. I was just spitballing, to see if there was a way to keep any propellant use to an absolute minimum, while still improving the rendezvous chances.Magico07noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-59106487536230962742015-07-04T10:03:41.878-07:002015-07-04T10:03:41.878-07:00Magico, gravity and inertia takes care of matching...Magico, gravity and inertia takes care of matching velocity and position. When the craft arrives at the platform, touchdown is as soft as feather.<br /><br />Some course adjustment would be needed since the moons' orbits are slightly inclined with regard to one another and the orbits are nearly but not perfectly circular.<br /><br />Perhaps a movable platform would give the ship more room for error. Notice that I have also suggested a movable entrance ramp. But I believe enroute vehicle course adjustments wwould be easy to do. Hop Davidhttps://www.blogger.com/profile/12923433894475072056noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-74016979519113935682015-07-04T03:06:58.508-07:002015-07-04T03:06:58.508-07:00Given the stated velocity differences, wouldn'...Given the stated velocity differences, wouldn't it be possible to extend the duration of the docking window by putting the docking mechanism onto a moving climber on the tether, to match height with the approaching vehicle? And/or by using a moving ballast-mass climber (above or below) to induce a controlled coriolis effect in the tether, to help match horizontal velocity differences, and potentially help damp them after docking? <br /><br />Thrusters on the docking vehicle, would only need to make fine adjustments for the final connection to the docking node, which should now match velocity fairly closely. I would suggest that this type of docking would be more akin to an air-to-air refueling rendezvous. Or perhaps something like this.<br /><br />http://www.theguardian.com/science/video/2009/jul/08/apollo-11-eagle-columbia-docking<br /><br />I should think that, once in reasonable proximity, a docking connection could be achieved within a 5 minute window.Magico07noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-37703964598705592742015-07-03T13:32:29.949-07:002015-07-03T13:32:29.949-07:00Doug, It's only I.S.S.-like near the balance p...Doug, It's only I.S.S.-like near the balance point where there's zero net acceleration. In the above example that'd be in the regions of Phobos or Demos' L1 and L2 points. After matching velocities, the ship would hang around and the robotic arm could grab it at it's leisure<br /><br />In other regions of the tether there is a net acceleration and rendezvous is not like docking with the I.S.S.. It is more akin to landing on a platform.Hop Davidhttps://www.blogger.com/profile/12923433894475072056noreply@blogger.comtag:blogger.com,1999:blog-3596550435682943926.post-7794243007135084282015-07-01T23:30:57.516-07:002015-07-01T23:30:57.516-07:00Let's say that the end of one tether has a Can...Let's say that the end of one tether has a Canadarm of 15 meters in length. How much time would the end of the other tether be within the reach of the Canadarm? Is this the right way of thinking about it? You liken it to docking at the ISS. In that situation the Canadarm has what, 20 minutes or so amount of time to grab a ship? Is that really an analogous situation?DougSpacehttps://www.blogger.com/profile/03057371106251356495noreply@blogger.com