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The database of precomputed missions is being updated after having recomputed all small-body orbits using the DE-441 planetary ephemeris. The database is expected to be fully up-to-date by May 15, 2021.
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Tutorial: Rendezvous Mission to 99942 Apophis

In this tutorial, we will show how to use the Design Interface to find mission opportunities to rendezvous with asteroid 99942 Apophis. This asteroid is relevant due to its very close approach to Earth on April 13, 2029 (see the close-approach data in CNEOS for more details). The FAQ section includes valuable information about common issues with the Design Interface. The duration of the mission is limited to 180 days.

The first step in the process is loading the mission-design data for 99942 Apophis into the Design Interface. Simply type its name (Apophis), IAU number (99942), designation (2004 MN4), or SPK-ID (2099942) in the search box at the top of the page (as shown in Figure 1), and press Enter to continue.

Find 99942 Apophis
Figure 1 - Using the search tool to find asteroid 99942 Apophis.

The interface will send an automatic request to the API server and retrieve both the set of pre-computed missions and the full-resolution pork-chop plot. The name of the asteroid will appear at the top of the page, followed by some static information about the orbit of the asteroid.

The data table with all the pre-computed mission options stored in the database can be found in the Mission Options section. Each record corresponds to one possible transfer. Initially, the table is sorted by ascending departure C3 (minimum C3 transfer appears on top). Each record is assigned a unique Id, starting from the end of the table. Figure 2 shows how the table looks when it is first loaded, with the Id, C3, and V dep. columns highlighted in red and green, respectively.

Table with mission options to 99942 Apophis (ΔV mode)
Figure 2 - Table with the set of pre-computed missions stored in the database (ΔV mode)

There are several buttons right above the table:

  • Download: download the data in the table as a CSV file, preserving the current order. Use this option when you are done adding new missions and need further post-processing, or simply for archival.
  • Select all: select all records in the table.
  • Deselect all: deselect all selected records in the table.
  • Plot trajectories: select one or two records and click this button to visualize the corresponding transfer orbits. By default, trajectories are displayed in the ICRF system using the ecliptic at J2000 as the reference plane. Change to the equatorial system using the drop-down menu above this button.
  • Delete selected: remove the selected records from the table.
  • ΔV mode: (selected by default) shows geometric information, as well as dates and ΔV requirements. Figure 1 displays information in ΔV mode.
  • Mass mode: switch to this mode to see the capabilities of different launch vehicles, instead of the parameters in ΔV mode.

Figure 3 shows a snapshot of the same table, but it has been switched to Mass mode. There is an upper limit to the maximum C3 that each launch vehicle can provide to a spacecraft with a reasonable mass. Given a certain transfer and a specific launch vehicle, if the C3 required by the transfer exceeds the maximum C3 of the launcher, the transfer will not be feasible. For example, Figure 5 shows a mission that will only be feasible if using Delta IV Heavy or SLS.

Table with mission options to 99942 Apophis (Mass mode)
Figure 3 - Snapshot of the mission-options table in Mass mode

The main element in the Mission Selection section is an interactive pork-chop plot (see Figure 4). By default, the plot displays contours for two parameters: departure C3 (blue-green filled contour levels), and arrival V-infinity (yellow-red contour lines). The horizontal axis on top/bottom shows the departure date from Earth in MJD/calendar format, respectively. The vertical axis on the left/right corresponds to the time of flight in days/years. Each of the blue dots corresponds to one of the missions listed in the data table.

Interactive pork-chop plot
Figure 4 - Interactive pork-chop plot

When hovering the mouse over the plot area, a tooltip will appear showing information about that particular point. In addition, there is a table under the pork-chop plot that will show the values of the rest of mission-design parameters for that particular mission (see Figure 5). If the mission is feasible (C3 < 150 km2/s2), you will be able to click on that point to add the corresponding mission to the table. An orange marker will appear to highlight the mission options selected by the user.

If the point you clicked on was not added to the table, check the HOVER INFO to find an explanation.

Extended information about the mission
Figure 5 - Extended information about the mission

The control panels shown in Figure 6 can be used to customize the pork-chop plot. On the left, there are five control buttons:

  • Update figure: after specifying the limits and format of the axes using the tools in the Contour Setup and Axis Setup menus, click this button to apply your changes.
  • Reset contours: reset the configuration parameters of the contour plots to their default values.
  • Reset axes: reset the configuration parameters of the axes to their default values.
  • Add new points: (active by default) when this mode is active, hovering the mouse over the plot area will display information about any point on the plot. You can then click on any point to add the corresponding mission to the table (as long as it is feasible, check the HOVER INFO tag for details).
  • Explore selected: switch to this mode to get information about the markers (either blue or orange), which correspond to the missions already listed in the table. If you want to select a new mission, switch to "Add new points" mode.

The Contour Setup menu gives you control over the contours that appear in the pork-chop plot. Use the drop-down menus to choose which parameters you want to be plotted. By default, the primary contour corresponds to the departure C3 and the secondary contour corresponds to the arrival V-infinity. If "Rendezvous" is selected, the plot will show the maximum mass that can rendezvous with the small body considering a two-impulse transfer. In this mode, the user must select one of the launch vehicles available in the corresponding drop-down menu. Switch the secondary to "None" if you want to see only one contour. You can also change the number of contour levels to be displayed (5, 10, 15, or 20), and the limits of the color bars.

The Axis Setup menu controls the axes limits. Use this panel to zoom into specific regions of the plot. You can also zoom in by clicking and dragging the mouse over a certain area of the plot or by dragging the slider. Use the drop-down menu to specify the launch period, which is five-years wide.

Controls for customizing the interactive pork-chop plot
Figure 6 - Controls for customizing the interactive pork-chop plot

To analyze the close approach of 99942 Apophis, we will follow these steps:

  1. Change the "Start year" to 2027, to be sure that we capture the 2029 close approach within the five-year window.
  2. Set the primary contour to "Rendezvous," and choose a launch vehicle from the drop-down menu. In this example, we will choose Atlas V (531).
  3. Set the secondary contour to "None," to simplify the visualization.
  4. Zoom in to analyze the time of closest approach in detail, and use the Axis Setup controls to limit the time of flight to 180 days.

Clicking the "Show visible only" button (right above the data table) filters the missions, and shows only the ones that appear in the figure after zooming. Switching to Mass mode and sorting the records by rendezvous mass (Rdzs) with Atlas V (531) reveals that the mission with Id 287 is the one that delivers the maximum mass (2445 kg) under the design constraints (see Figure 7).

Finding the mission that maximizes the rendezvous mass
Figure 7 - Finding the mission that maximizes the rendezvous mass

The mission can be located in the plot using the "Selected only" mode. We will then switch back to "Add new points" mode and explore neighboring missions seeking better solutions. In particular, we found a mission that delivers 2455 kg to the asteroid in just 70 days. Clicking on that mission added it to the table with Id 605, as shown in Figure 8. The spacecraft will be launched on March 31, 2029, and it will arrive at Apophis on June 9, 2029.

Rendezvous opportunities
Figure 8 - Rendezvous opportunities

The Launch-Vehicle Selection tool is useful for finding the optimal launch dates when the goal is to maximize the mass delivered to the small body. The figure shows, for different launch dates, the maximum mass that can reach the target using different launch vehicles. The two buttons in the Select Mission Type menu allows the user to change from flyby mode to rendezvous, and vice-versa. Using the Select Launch Vehicle table, you can select the vehicles you are interested in, and click the "Update selection" button to apply the changes. You can zoom into specific launch-date intervals by clicking and dragging on the plot, or by using the range slider just under the plot. Click the "Reset view" button to go back to the original view.

To analyze the example under consideration, we will first switch to rendezvous mode ("Rdzvs"), select only Atlas V (531) from the list, and then click "Update selection" (see Figure 9). After zooming into the same area as Figure 8, it is easy to locate the mission that maximizes the rendezvous mass. When hovering the mouse over that point, the data in the table reveals that it is the same solution that we already added to the table with Id 605. If we tried to click on the Launch-Vehicle Selection plot to add it to the table again, the HOVER INFO would tell us that the mission already exists in the table.

Maximum rendezvous mass as a function of the launch date
Figure 9 - Finding the maximum rendezvous mass using the launch-vehicle selection tool

FirstGov 2021-May-08 08:49 UT 
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