Fascinating stuff!! Mars Helicopter - Balancing Risks

Fascinating stuff!!
24 flights so far.

Go to the citation for the video, pictures and graphs:

https://mars.nasa.gov/technology/helicopter/status/373/balancing-risks-in-the-seitah-region-flight-24/

STATUS UPDATES | April 05, 2022
Balancing Risks in the 'Séítah' Region - Flight 24
Written by Ben Morrell, Ingenuity Operations Engineer at NASA's Jet 
Propulsion Laboratory
This annotated overhead image from the HiRISE camera aboard NASA’s Mars 
Reconnaissance Orbiter (MRO) depicts three options for the agency’s Mars 
Ingenuity Helicopter to take on flights out of the “Séítah” region, as 
well as the location of the entry, descent, and landing (EDL) hardware.
Mars Helicopter Route Options out of ‘Séítah': This annotated overhead 
image from the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter 
(MRO) depicts three options for the agency’s Mars Ingenuity Helicopter 
to take on flights out of the “Séítah” region, as well as the location 
of the entry, descent, and landing (EDL) hardware. Credits: 
NASA/JPL-Caltech/University of Arizona/USGS. Download image ›
Ingenuity continued its journey towards the river delta this weekend 
with Flight 24. This flight took place Sunday, April 3, and the data 
arrived back later that evening. The flight was the fourth of five 
sorties Ingenuity will make to cross the “Séítah” region of Jezero 
Crater and arrive in the vicinity of its delta. This multiflight 
shortcut across Séítah is being done to keep ahead of the Perseverance 
rover – which is currently making great time on a more circuitous route 
to the same area.

The Ingenuity and Mars 2020 teams have big plans for the helicopter at 
the delta. But they have to get there first, and prior to Flight 24 a 
crucial decision had to be made on which of three different flight plans 
offered the best chance of a successful delta arrival.

The three options on the table were:

Option A: a single, long flight.
Option B: two shorter flights.
Option C: a very short Flight 24 to make the long flight out of Séítah 
slightly easier than option A.
In deciding which of these options to greenlight, the Mars Helicopter 
team had to consider multiple factors: thermal, atmospheric conditions, 
flight time, drift, landing sites, and keeping up with the rover. We'll 
explore each of these factors and what role they played in the overall 
risk assessment and selection of our decision.

Thermal Limitations

For spacecraft, “thermal” refers to the management of the temperatures 
of each component. Every part of Ingenuity has what is called Allowable 
Flight Temperatures (AFT), which give a range of temperatures at which 
each part is safe to operate. Even your phone or computer has a 
recommended temperature range: Too cold or too hot and it will not work 
as intended. Keeping “within AFTs” is critical for ensuring the health 
of Ingenuity, which means we are very careful to manage this –  for 
example, by using heaters overnight when it is cold, and limiting 
activities during the day, when it is warmer. A particular challenge for 
Ingenuity is managing the temperature of its actuators, the servos and 
motors that allow it to fly (see some of these here). These components 
generate a lot of heat during flight, to the extent that the maximum 
flight time is often limited by the maximum AFT of these actuators.

Atmospheric Seasonal Conditions

If you have been following this blog, you will know that we have been 
operating with reduced air density since September, requiring an 
increase in rotor rpm from 2,537 to 2,700. Flight 14, for example, was a 
checkout flight to confirm Ingenuity could fly in these conditions. For 
all flights since then, Ingenuity has been successfully operating with 
2,700 rpm. Unfortunately, though, using a higher rpm causes the 
actuators to heat more rapidly and reach their AFTs sooner, limiting 
maximum flight time. Practically, this has limited us to flights of 130 
seconds or less. Thankfully, we are toward the end of the Martian 
summer, with its low air density, and starting to move into the Martian 
fall, with higher air densities (see below), meaning we can now return 
to the 2,537 rpm of our first 13 flights. This change in rpm allows an 
increase in flight time to approximately 150 seconds. However, 
atmospheric density isn't the only factor at play: The main driver of 
the changes in density is the temperature of the atmosphere, which also 
has a major impact on – you guessed it – the temperature of Ingenuity.

It is warmer now coming out of the summer than with our earlier flights 
in the spring. So even though we have been flying at 10:00 a.m. local 
mean solar time (LMST)- on Mars throughout the summer, Ingenuity has 
been hotter than flights at 12:00 LMST in the spring. A warmer 
atmosphere means warmer components, meaning we reach maximum AFTs 
sooner. This means, flying at 10:00 LMST, we still can't fly for as long 
as we did previously, such as during Flights 9, 10, and 12.

Models for the seasonal variation in atmospheric density on Mars between 
summer (low density) and winter (higher density) predict that air 
density will be high enough in late March for NASA's Mars Ingenuity 
Helicopter to return to its original RPM.
Mars Atmosphere Density Model: Models for the seasonal variation in 
atmospheric density on Mars between summer (low density) and winter 
(higher density) predict that air density will be high enough in late 
March for NASA's Mars Ingenuity Helicopter to return to its original 
RPM. Credits: NASA/JPL-Caltech. Download image ›
Flight Time and Distance

With the current atmospheric conditions at Jezero Crater, the AFTs of 
the actuators are the limiting factor for the total flight time. Let's 
take a more detailed look at the different options for Flight 24 and beyond:

Option A: The long flight out of the delta requires 170 seconds of 
flight, the maximum of our previous flights. This is not possible until 
the atmosphere cools down further.
Option B: The two shorter flights are operating the same as our previous 
“summer” flights: 130 seconds of flight time. This flight time is 
possible without any changes.
Option C: The first flight, a short hop, is designed to reduce the 
flight time needed for the second flight to 160 seconds. This is 
possible if we: i) reduce the rpm to 2,537, and ii) fly earlier in the 
sol to have lower atmospheric temperatures.
The team determined that by flying 30 minutes earlier, at 09:30 LMST, 
the flight time could be increased by 10 seconds. However, Ingenuity had 
never flown at 09:30 LMST before, so this would be a new “first.” And 
flying earlier brings with it associated risks with the charge state of 
the helicopter's batteries: Ingenuity uses power to heat itself 
overnight and recharges its batteries with its solar panel, meaning the 
batteries have less charge in the morning. If we choose to fly at 9:30, 
we would first have to test it out – waking Ingenuity at this time 
without flying, to check that it would have sufficient charge for a flight.

In summary, the different maximum flight time options available are:

130 seconds (baseline)
150 seconds (decreased rpm)
160 seconds (decreased rpm and earlier flight time)
Flight time is normally equivalent to distance traveled, but it also 
depends on the maneuvers being performed. For example, rotating in place 
(called “yawing”), is done (at least at Mars) slowly, taking a handful 
of seconds with no distance traveled. For that reason, Mars Helicopter 
flights with more yaw maneuvers don't travel as far in the same flight time.

All these factors come into play with option C – the short hop. This 
flight would enable the longer 160 second flight, for several reasons: 
1) it is a check-out test for flying back at 2,537 rpm, 2) it is a test 
for flying at 09:30 LMST, and 3) it reduces the flight time for the 
subsequent flight by doing the time-consuming yaw maneuvers and moving 
slightly closer to the target for the second flight. All three of these 
steps are required to enable a 160-second flight out of the Séítah.

Drift

As discussed in previous blog posts, Ingenuity was a tech demo expecting 
to fly over flat ground. When flying over “non-flat” terrain such as 
hills, cliffs, large boulders and large dunes, Ingenuity's estimate of 
its position and heading can drift. This drift leads to a wider area 
where it may land, called the landing ellipse. The farther it flies, the 
larger the potential drift, and the larger the landing ellipse. The 
Séítah region has many of these non-flat features (see the dunes and 
rocks in the image at the top, or on the interactive map), making it 
riskier for Ingenuity to fly over this region. An additional challenge 
with the upcoming flights is the presence of hardware from 
Perseverance's entry, descent, and landing (EDL), including the sky 
crane, parachutes and backshell. The green dots (in figure 1) show the 
predicted locations of this hardware from orbital imagery. Some of these 
components are under the flight path of option B, which presents a 
potential for unexpected performance from Ingenuity's laser altimeter (a 
laser that measures the helicopter's height above the surface) and 
visual odometry system, which could cause more drift.

Landing Sites

Each flight of Ingenuity has a planned landing ellipse (or sometimes 
just a landing region) that has been analyzed to be safe to touch down 
on, and to be large enough for the expected drift. The challenge is 
finding a large enough landing area that is free of hazards, such as 
rocks, large slopes, or even EDL hardware. Finding large landing sites 
is challenging in Séítah, so shorter flights are preferred, to reduce 
the potential drift, and hence reduce the required size of the landing 
ellipse. Outside of Séítah, the terrain is relatively flat and 
helicopter-friendly, allowing for large landing ellipses and long 
flights with greater drift. Let's look at the different options and 
their landing sites:

Option A: one landing ellipse outside of the Séítah that is large and safe.
Option B: The landing ellipse for Flight 24 is within the Séítah, 
limiting its size, and requires a medium-distance flight, given less 
margin and making it slightly riskier than landing outside the Séítah.
Option C: The first landing site (for Flight 24) requires only a short 
flight, reducing the amount of potential drift, and it remains within 
the relatively large landing ellipse of the previous flight, 23.
Keeping up With the Rover

Perseverance is making great progress on its drive to the river delta, 
and it is important that Ingenuity keeps pace to arrive at the delta 
before the rover does. This is for two reasons: telecommunications and 
safety. Ingenuity only communicates with the helicopter base station on 
Perseverance, so it needs to stay close enough to have a good 
connection. For safety, it is ideal if Ingenuity flies ahead of 
Perseverance to avoid ever having to fly past or near the rover, to 
minimize the risk of any close contact in a worst-case scenario.

Balancing Risks

Let's review each of the factors above to see which option gives the 
best set of trade-offs to balance risk:


Factors
Option
RPM
Time of Sol
Drift / Landing Site
Keeping With Rover
A
2,537 (change)
N/A. Too hot
No landing in Séítah
Have to wait
B
2,700
10:00 (no change)
Medium flight in Séítah;

EDL hardware risk
On pace
C
2,537 (change)
09:30 (new!)
A short flight in Séítah
On pace
Which option would you choose?

As is often the case in Ingenuity operations, there is no obvious 
solution that is the best for all factors: Trade-offs have to be made 
based on the available data and the judgment of team members. In this 
case, the helicopter team decided to go with option C.

Flight 24 Summary

With option C, flight 24 was a short hop and yaw at 09:30 LMST with 
2,537 rpm, and set us up to exit Séítah on flight 25.

Flight #: 24
Goals: Test flight at 2,537 rpm, 09:30 LMST flight
Altitude: 10 meters
Time aloft: 69.5 seconds
Distance: 47 meters
With Flight 24 in our log book, it is now time to look forward to our 
upcoming effort that charts a course out of Séítah.  Flight 25 – which 
was uplinked yesterday - will send Ingenuity 704 meters to the northwest 
(almost 80 meters longer than the current record - Flight 9). The 
helicopter's ground speed will be about 5.5 meters per second (another 
record) and we expect to be in the rarefied Martian air for about 161.5 
seconds.

See you at the delta!