SSI-41 Crosses Continental US & Breaks World Record

SSI is always proud to showcase our team's launches.


Today, we're especially proud of SSI-41.


SSI-41 is the flight of ValBal Mk 5.1, a slight revision to the ValBal Mk 5 vehicle flown just over a month ago. The Mk 5 vehicle, an enormous improvement over Mk 4, managed to fly its way to Mexico over the course of a 16 hour journey, and landed due to power anomalies.


The response to the power anomalies and other imperfections in the Mk 5 vehicle came in the form of Mk 5.1 — a vehicle that would fly for a distance of over 3,500 miles, spanning the entire North American continent, for over 70 hours, to bravely adventure where no latex high altitude balloon has ever gone before.

Background


ValBal, short for "Valve-Ballast" is a novel platform developed by the SSI Balloons team that utilizes a gas venting valve and a ballast dispenser to zero its ascent rate and maintain a nearly constant altitude. Conceived in the winter of 2014, ValBal has been in development and testing for over a year and a half. ValBal first equilibrated at altitude in SSI-18, traversed state lines in SSI-21, flew to Canada in SSI-22, and landed in Mexico in SSI-38. 


The motivation for the development of such a platform is simple. In the realm of high-altitude ballooning, latex balloons are by far the most affordable, starting at tens of dollars and costing at most a few hundred dollars. However, latex balloons, by their very nature, are designed for short term flights -- most often, to fly a payload to near-space altitudes, followed by the burst and descent of the balloon. This class of flight typically lasts no more than three hours and travels less than 100 miles. By contrast, more expensive balloon technology, such as Zero Pressure and Super Pressure balloons, are capable of flying for long durations of time, but at the cost of thousands to millions of dollars per flight. Thus, ValBal was developed to provide research payloads with affordable access to long-duration flights in a near-space environment.

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The Launch

SSI-41 was scheduled for launch on the evening of Tuesday, June 14th. The team arrived at the launch site (Laird Park, near Modesto CA) at approximately 9:45 PM PDT. After setting up all of the necessary equipment, the team began the process of vehicle pre-flight verification. After preliminary testing of vehicle sub-systems, including valve, ballast, and flight controls, the system passed pre-flight verification. The team spent considerable time verifying satellite communications -- a crucial vehicle system. Satellite communications allow the team to receive data from the payload over the Iridium satellite constellation, and also uplink commands to the payload for altitude controller adjustments, power distribution management, and other performance alterations.


After unfortunately long delays in communications intervals, the vehicle was cleared for launch. The team began filling of the 1500g Kaymont Latex balloon, and, once filled, attached the ValBal Mk 5.1 vehicle to the neck of the balloon and filled the payload with ballast. The payload was finally released at 4:18 AM PDT, June 15th.

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The Flight

Upon release, the payload registered a nearly 5 m/s ascent rate. The first step in flight is a successful equilibration at altitude, making the initial ascent of the vehicle one of the most crucial windows of the mission. As several lifting-gas releases were reported over satellite communications, the payload continuously decreased its ascent rate, equilibrating at 6:37 AM PDT at approximately 12,500 m. 


ValBal operates around a designated setpoint altitude. About this altitude, it is allowed to oscillate within specified flight ceiling and floor bounds. As it approaches either the ceiling or the floor, it is incentivized to either vent gas or dispense ballast to compensate its rate of ascent and return to setpoint altitude. Although the system actively controls the valve and ballast sub-systems to maintain altitude, there are in fact long periods of inactivity when the system is able to reach nearly neutral buoyancy. During SSI-41, ValBal experienced extremely long windows of system stability, not needing to vent or ballast significantly to maintain altitude. 


The payload continued a nominal flight, beginning with a north-east heading and flying through Nevada, Idaho, Wyoming, and Montana before entering Canadian airspace at 6:23 PM PDT on June 16th. The payload continued its flight through the Saskatchewan, Manitoba, Ontario, and Quebec provinces until a return to United States airspace at 1:21 PM PDT on June 17th. At this point, the payload had surpassed 57 hours and 2 minutes aloft, the previous world record for latex balloon fight time, set by the California Near Space Project's CNSP-11 launch. ValBal flew over 3,000 miles and continued on a south-east trajectory through New York state, crossing the continental United States.
At 2:28 AM PDT, June 18th, the payload landed in the northern Atlantic Ocean. It flew for a final total distance of 3565 miles, setting a new latex balloon record flight time of 70 hours, 10 minutes.
Altitude Over Time

Custom Built Hardware

All iterations of ValBal have been built around custom-made avionics and mechanical systems. The v5.1 avionics suite consists of two printed circuit boards, a battery pack and main flight computer, designed by SSI team members using Altium Designer, which was graciously provided to SSI by our platinum-tier sponsor, Altium Ltd. The balloon's mechanical systems consist primarily of a laser cut acrylic structure, with the avionics, batteries, and recovery GPS housed in a styrofoam enclosure further insulated with fiberglass-aerogel composite. The valve and ballaster are actuated by two external motors, which SSI modified and qualified for cold operation.
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Mission Control Suite (HABMC)


The flight of SSI-41 would have been tremendously harder to visualize and control without the aid of habmc, an SSI-internal mission control suite developed by SSI Balloons team member Kai Marshland. habmc processes all satellite communication data, handles parsing, data visualization, mapping, airspace and weather overlays, and tremendously more. The suite is new in 2015 and has allowed all of SSI and hundreds of on-lookers to track the payload during its flight. For those interested in tracking the payload as it flies, as well as tracking future payloads, visit habmc.stanfordssi.org.
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Future

The flight of SSI-41 is an exemplary case of the capabilities of the ValBal system for long duration missions. The entire system comes at a low cost of only hundreds of dollars for the mechanics, electronics, and flight balloon. By comparison, zero pressure balloons typically cost no less than $1,000 and do not include avionics, power, communications, or gas. ValBal is also significantly more capable than a zero pressure balloon, as it can equilibrate at virtually any altitude between 10 and 25km as required by an onboard experiment or to catch favorable winds. The vehicle can fly for multiple days continuously at a specified altitude, collecting data over time.


In the future, the ValBal vehicle will continue to be pushed for increasing levels of endurance, and be more readily equipped to carry research payloads in an on-board payload bay. Targetting payload masses on the order of 1 kg, the team has envisioned atmospheric research, weather tracking, near-space biological experiments, and other payloads, and is interested in collaborating with researchers seeking to conduct high altitude studies.


An additional future goal of the team, as a display of system capability, is to fly ValBal in a journey to circumnavigate the planet, launching from California and recovering on the western coast of North America.