TriDAR

Key takeaways

TriDAR belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect TriDAR to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TriDAR from memory before moving on to harder problems.

Reference excerpt

TriDAR, or Triangulation and LIDAR Automated Rendezvous and Docking, is a relative navigation vision system developed by Neptec Design Group and funded by the Canadian Space Agency and NASA. It provides guidance information that can be used to guide an unmanned vehicle during rendezvous and docking operations in space. TriDAR does not rely on any reference markers positioned on the target spacecraft. Instead, TriDAR relies on a laser based 3D sensor and a thermal imager. TriDAR's proprietary software uses the geometric information contained in successive 3D images to match against the known shape of the target object and calculate its position and orientation. TriDAR made its inaugural demonstration space flight on board Space Shuttle Discovery on the STS-128 mission, launched on 28 August 2009. On STS-128, TriDAR provided astronauts with real-time guidance information during rendezvous and docking with the International Space Station (ISS). It automatically acquired and tracked the ISS using only knowledge about its shape. This marked the first time a 3D sensor based "targetless" tracking vision system was used in space.

Background To date, most operational tracking solutions for pose estimation and tracking on-orbit have relied on cooperative markers placed on the target object(s). The Space Vision System (SVS) used black on white or white on black dot targets. These targets were imaged with Space Shuttle or International Space Station (ISS) video cameras to compute the relative pose of ISS modules to be assembled. The Trajectory Control System (TCS) was used on board the space shuttle to provide guidance information during rendezvous and docking with the International Space Station (ISS). This laser-based system tracks retro reflectors located on the ISS to provide bearing, range and closing rate information. While reliable, target based systems have operational limitations as targets must be installed on target payloads. This is not always practical or even possible. For example, servicing existing satellites that do not have reflectors installed would require a targetless tracking capability.

STS-128

TriDAR was tested in space for the first time on board Space Shuttle Discovery during the STS-128 mission to the ISS. The objective of the test was to demonstrate the capability of the TriDAR system to track an object in space without using targets markers such as retro-reflectors. For this mission, TriDAR was located in the payload bay on the Orbiter Docking System (ODS) next to the Shuttle's Trajectory Control System (TCS). The system was activated during rendezvous when the Shuttle was approximately 75 km (47 mi) away from the ISS. Once in range of the 3D sensor, TriDAR automatically determined bearing and range to the ISS. During rendezvous, TriDAR entered shape based tracking which provided full 6 degree of freedom guidance and closing rate. Key system information was provided in real-time to the crew via enhanced docking displays on a laptop computer located on the shuttle's crew compartment. The system was designed to perform the entire mission autonomously. It self-monitored its tracking solution and automatically re-acquired the ISS if tracking had been lost. TriDAR was also tested during undocking and fly-around operations.

STS-131

TriDAR was again carried on board Space Shuttle Discovery during the STS-131 mission to the International Space Station. The TriDAR operated during shuttle rendezvous with the ISS, and acquired useful data up till the shuttle R-bar Pitch Maneuver. At that point, a cabling issue resulted in a loss of communications. Using a backup cable for undock and flyaround, the TriDAR operated "flawlessly", according to flight director Richard Jones.

STS-135 TriDAR was on board Space Shuttle Atlantis during the STS-135 mission to the International Space Station.

Capabilities TriDAR builds on recent developments in 3D sensing technologies and computer vision achieving lighting immunity in space vision systems. This technology provides the ability to automatically rendezvous and dock with vehicles that were not designed for such operations. The system includes a 3D active sensor, a thermal imager and Neptec's model based tracking software. Using only knowledge about the target spacecraft's geometry and 3D data acquired from the sensor, the system computes the 6 Degree Of Freedom (6DOF) relative pose directly. The computer vision algorithms developed by Neptec allow this process to happen in real-time on a flight computer while achieving the necessary robustness and reliability expected for mission critical operations. Fast data acquisition has been achieved by implementing a smart scanning strategy referred to as More Information Less Data (MILD) where only the necessary data to perform the pose estimation is acquired by the sensor. This strategy minimizes the requirements on acquisition time, data bandwidth, memory and processing power.

Hardware The TriDAR sensor is a hybrid 3D camera that combines auto-synchronous laser triangulation technology with laser radar (LIDAR) in a single optical package. This configuration takes advantage of the complementary nature of these two imaging technologies to provide 3D data at both short and long range without compromising on performance. The laser triangulation subsystem is largely based on the Laser Camera System (LCS) used to inspect the Space Shuttle's thermal protection system after each launch. By multiplexing the two active subsystem's optical paths, the TriDAR can provide the functionalities of two 3D scanners into a compact package. The subsystems also share the same control and processing electronics thus providing further savings compared to using two separate 3D sensors. A thermal imager is also included to extend the range of the system beyond the LIDAR operating range.

Applications

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with TriDAR

Start with the simplest possible case. Write down what TriDAR claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to TriDAR before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about TriDAR ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of TriDAR

In research: TriDAR appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses TriDAR in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: TriDAR is common in secondary-school and first-year university syllabi. It links to neighbouring topics Canadian inventions, Space Shuttle program, Space program of Canada, so understanding it makes those chapters shorter.
In everyday life: Look for TriDAR outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study TriDAR in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TriDAR means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain TriDAR out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TriDAR in simple terms?

TriDAR, or Triangulation and LIDAR Automated Rendezvous and Docking, is a relative navigation vision system developed by Neptec Design Group and funded by the Canadian Space Agency and NASA. It provides guidance information that can be used to guide an unmanned vehicle during rendezvous and docking…

Why does TriDAR matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study TriDAR?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on TriDAR.