NMEA 2000 Explained

["What this doesn't address is the fact that just becasue the NMEA 2000 network is powered you still will have to run the power cable for chartplotter or a GPS combo unit as the NMEA backbone, as this video states, doesn't have much power. When I installed my NMEA 2000 network I was under the assumption that the NMEA network would power all my stuff and there would be no need for the original power supply to be ran to back of chartpotter and other bigger units. great video but addressing what was said above would be great." -- "You can only give power to the little displays with the nmea alone." - /YouTube comments/]
 
"NMEA 2000 (IEC 61162-3) is a low cost, moderate capacity (250 K- bits/second), bi-directional multi-transmitter/multi-receiver instrument network to interconnect marine electronic devices. /1/

Figure 1. NMEA 2000 network.

The NMEA 2000 standard contains the requirements for the minimum implementation of a serial-data communications network to interconnect marine electronic equipment onboard vessels. Equipment designed to this standard will have the ability to share data, including commands and status, with other compatible equipment over a single signaling channel.

Figure 2. Networking a ship.

Increasingly, modern marine electronic equipment requires data from multiple sources to enable the host of features and function that can be available to the mariner. Without a network standard to provide this data integration, equipment designers must provide multiple data inputs, which involve expense and additional wiring, or use devices that “merge” data onto a single channel. Individual systems on a vessel, such as engine machinery or navigation systems, perform relatively dedicated functions, often have real- time requirements measured in milli-seconds, and need fewer connected nodes. These systems tend to be smaller and more self-contained when compared to other vessel networks, and carry less data volume. Because this network application integrates inexpensive sensors and actuators into larger systems, the cost per node must be far less than in other shipboard applications. This network application is addressed by NMEA 2000 (IEC 61162-3).

YouTube video: "How NMEA 2000 Network Works"

Figure 3. A basic NMEA 2000 network.

NMEA 2000

Architecture:

• Bus (parallel) wiring configuration using 4-conductor twisted- pair wire to carry power to operate the interface and data signals.
•  Linear network with end terminations and multiple short-length drop cables connecting the backbone cable to individual nodes.

Operation:

• Network access: Carrier Sense/Multiple Access/Collision Arbitration using CAN (Controller Area Network).
• Multi-master network operation (no central control node).

 Self-configuring.

• Special network tools, desirable for diagnostic purposes, are not necessary for operation.

Size:

• •Physical nodes: Up to 50 connections. 
• Functional nodes: Up to 254 network addresses. 
• Length: Up to 200 meters (at 250kbits/second bit rate).

At the basic level, and in wide use, the older NMEA 0183 (IEC 61162-1) provides serial data distribution from a single transmitter to multiple receivers. Operating at 4800 bits/second this protocol has the capability of delivering approximately ten messages, or sentences, per second. This has generally proven adequate when a single device is broadcasting data for use by other equipment. But it quickly reaches a limit when systems start to combine data. However, its use is expected to continue well into the future for simpler applications, redundant or backup data connections, and when direct device-to-device connections are needed.

YouTube video: "NMEW 2000 Network Guide Video"


 
THE PHYSICAL LAYER

This layer defines the electrical and mechanical aspects of the physical link between network connections, and references characteristics of the CAN devices and network interfaces to be used in NMEA 2000. 

Figure 4. Shipboard networks and interfaces.

The electrical characteristics of the physical layer are dictated by the following:

• Media access uses CAN as defined by ISO 11898, Road Vehicles - Interchange of Digital Information, Controller Area Network (CAN) for High-speed Communication. 
• CAN utilizes dominant/recessive bit transmission.
• Time delays and network loading limit bit rate and network length.
• Differential signaling improves noise immunity.
• Network single-point common signal reference controls ground voltage levels and reduces RFI.
  

Differential signaling indicates that powered interface circuits and a signal-reference common to all nodes on the network is required. A single-point common reference is specified in order to avoid radio-interference caused by ground loops and to maintain control of ground-voltage levels between nodes such that they remain within the common-mode range (approximately +/-2.5 Volts) of the network transceiver circuits. An important change from previous draft versions allow the use of the vessel’s 12-Volt battery to power the network, if the length of the backbone cable and the number of nodes are small enough, instead of the use of a more expensive regulated power supply that was previously required. 

Figure 5. Typical ground loop problem solved with optically isolated network.

Single-point power and common may be distributed via the network backbone cable as previously required, or for heavier current, by dedicated twisted-pair wires to individual devices. This feature allows equipment to draw additional operating current from the network power source and to be built with minimum interface complexity. In all cases the power and common for the interface circuits must not connect to other power or ground in a network device. This isolation may be achieved in a number of ways. One is by use of isolation circuits (e.g., optoisolators) within the device, either at the interface or at specific places where the equipment connects to other devices. Another way is by assuring that no power or ground connections, other than the network power and network common, connect to the device. The latter method is suitable for equipment such as displays or sensors that have no interfaces other than with the NMEA 2000 network, can draw all of their operating current from the network source, and have isolated packaging and mounting designs.

The figure below illustrates a typical physical layer interface circuit using available transceiver integrated circuits meeting the requirements of ISO 11898. Ground isolation, illustrated with optoisolators, is shown between the network and the CAN controller and other device circuits (e.g., microprocessor and other circuits). However, as pointed out above, isolation from other circuits may be accomplished by other means. 

Figure 6. Typical optically isolated network interface.

The illustrated transceiver circuit requires regulated +5 Volt power that is provided by the Regulator and Protection circuits. The purpose of the protective circuits is to prevent damage to the regulator and the interface circuits from overvoltage and reverse voltage. No permanent damage should result from a voltage level of +/-18.0 Volts or less applied between any two wires in the interface for an indefinite period of time or from miswiring the interface lines in any combination.


YouTube video: "Tips - Installing a NMEA 2000 Backbone on a Boat"


THE MAIN POINTS OF THE PHYSICAL LAYER

Environmental and Radio Frequency Interference

NMEA 2000 implementations must meet the Durability and Resistance to Environmental Conditions described in Section 8 of IEC 60945 and meet the Unwanted Electromagnetic Emissions and the Immunity to Electromagneic Environment conditions of Sections 9 and 10 of IEC 60945. Shielded cables are recommended, and may be necessary to meet these latter requirements.

Ground Isolation

AC and DC isolation is required between all of the terminals at the interface connector, with the network cables disconnected, and any other ship’s ground or voltage sources. As discussed above this can be accomplished with isolation devices such as opto-isolators or by wiring and packaging design. For most applications, except those with very low power needs, the isolated interface is the preferred implementation.

Network Signaling

The two signal lines carry differential signals measured with respect to the network power common. The signals on the network represent two states: Dominant state or Logic ‘0’, and Recessive state or Logic ‘1’, during the transmission of the Dominant state by one or more nodes the state of the network is Dominant. The interface must be designed so that the signal lines are in the Recessive state when node power is off.

The AC and DC voltage parameters of the network signals are specified by ISO 11898. The nominal voltage levels are:

• Dominant state:
 CAN+ = 3.5V CAN- = 1.5V V diff = CAN+ - CAN- = 2.0V

• Recessive state:
 CAN+ = 2.5V CAN- = 2.5V V diff = CAN+ - CAN- = 0.0V

• Common Mode range: Difference in network common voltage between nodes:
 -2.5 to +2.5 Volts

Network Power

The interface circuits must operate over the range of 9.0 to 16.0 Volts DC. The voltage for the interface can either be supplied from the network backbone cable or supplied by a dedicated twisted-pair power cable connected only between a single node and the network power source (the vessel’s battery or one regulated power supply). The amount of current delivered by the network cable is limited. When a dedicated power connection is used the node is allowed to draw additional current but the connections must be labeled, and physically separated and isolated from other power and ground connections. Under no condition may the node power or ground be connected to other power or ground in the equipment.

To aid in planning network installations manufacturers are required to specify the power rating for each connected device as a “load equivalency number”. The actual power source for the network can be either a single-point connection to the vessel’s battery or one or more isolated power supplies distributed along the network. The size and routing of the cables must be carefully considered. As the number of nodes with high load equivalency number increase, DC voltage loss in the cables quickly becomes the limiting factor for network length rather than the propagation time for the signals. For networks of shorter length and with a lower number of connected devices the ship’s battery may be used to power the network nodes directly. In place of the battery, electrically isolated regulated power supplies may be used if it is necessary to extend the size of the network.

Cables and Connectors

Two methods are provided for connecting to the network backbone cable: a standard connector or barrier strips. These connections are used for connecting segments of backbone cable together, for connecting terminations at the two ends of the cable, for connecting the network power source, and for connecting nodes. The drop cable, the short cable running from the backbone connection to the node equipment, may connect to the equipment anyway the manufacturer chooses. It is the connections at the backbone that are controlled by the NMEA 2000 standard. 

Figure 7. Typical "star" configuration. (The actual network is a short stub and all the devices connect to it with longer cables.)

Barrier strips are only recommended when the connections are made in a protected location, or when they are installed in a weatherproof enclosure, thus meeting the requirements for Resistance to Environmental Conditions for exposed equipment in IEC 60945. Barrier strips positions must be either numbered or color-coded in accordance with the definitions in the standard.

The connector selected for the NMEA 2000 backbone is a 5-pin type used in industrial networks and is available from multiple sources (including Molex, Turck Inc., Methode Components, and Daniel Woodhead Company). The connector is available as a 3-port “T” connector, cable-end connector, bulkhead-mount connector and special configurations with internal termination resistors.

YouTube video: "How to Install NMEA 2000 Boat Electronics System"

Cable specified for the network must meet both the characteristic impedance and propagation delay requirements for use as a transmission line, and also the wire-size needs of the DC power distribution function of the cable. The cable lengths on the network, the number of nodes connected, the distribution of the nodes, and the location of the power source connection(s) into the backbone cable determine the actual cable requirements in a particular installation. Two cable sizes are specified and can be used as needed in an installation. NMEA 2000 Heavy cable is 5-wire consisting of two shielded- twisted-pairs and a common shield drain wire. The wire pairs are No. 16 AWG (1.33 sq. mm) for DC power and No. 18 AWG (0.83 sq. mm) for signals. NMEA 2000 Light cable uses No. 22 (0.38 sq. mm) and No. 24 (0.24 sq. mm) respectively.

The cable specified has a defined color code, in the event that these colors are not available the substitute cable must be marked according to the standard."
 

Figure 8. Typical connectors, running power and signal.

 ["The solution to ground loop noise is to break the ground loop, or otherwise prevent the current from flowing. The diagrams show several solutions which have been used " (Read more about ground loops.] 

[Below is an interesting video about the NMEA 2000 networking problems. In this case it is about the fact that there can only be one terminating resistor in the network at each end of it (2 all together). (And also other installations problems.)]

YouTube video: "Mast Climbing Madness (Sailing Giraffe)"



RESOURCES


/1/ Cassidy, Frank - "NMEA 2000 Explained - The Latest Word" - 1999 


/2/ Wikipedia


                                    * * *

JB11 Latest Jetpack

Looks like Jetpack people have again created a new version of their "real jetpack", real meaning that it really uses jets and not rockets like some earlier versions of jetpacks did.

Figure 1. Jetpack JB-11 uses multiple turbines for additional redundance. It can fly with one turbine inoperative. 

VIDEOS:

YouTube video: "World’s Most Advanced JetPack, the JB11 First EVER Flight at Goodwood Festival of Speed 2018"


RESOURCES:

/1/ http://www.jetpackaviation.com/

/2/ YouTube

* * *

Mars 2020 Rover

[NASA will send a new rover to Mars year 2020 and also return some samples from Mars to Earth. The rover is similar to the Curiosity rover already there. Here are some facts about it - the video link at the end of this post is rather informative. /1/ /2/]

Figure 1. Computer-Design Drawing for NASA's 2020 Mars Rover

Apollo On-board Guidance History (Part 16, Apollo Control Systems)

[This article is based mainly on D.G. Hoag's paper about Apollo's on-board Guidance, Navigation, and Control System history /10/]

APOLLO ON-BOARD GN(et)CS HISTORY /10/

"This account is written from the point of view of one who experienced the hectic but exciting years. An enormous amount of material has been left out for practical reasons, and many worthy names regretfully remain unmentioned. Technical details have been deliberately played down: they can be found in the bibliography. The overall message is simple: In an incredible and audacious task, the landing of men on the moon, the guidance equipment for the mission was created out of primitive principles, prolific imagination, and a lot of hard work." -- Hoag, D.G.

The Beginnings /10/

"The forerunner of the Apollo guidance, navigation, and control system (GNetCS)), is found in an unmanned spacecraft and mission study started in 1957 by the Instrumentation Laboratory at MIT under a contract with the Air Force Ballistic Missile Division.

Milton Trageser (left), Hal Laning and Richard Battin

DSKY Hardware (Part 15, Apollo Control Systems)

[Since it looks like that DSKY is very popular with its companion LGC (or AGC) I add this article to fully cover the DSKY hardware (as it was 1966) in its detail. DSKY was a small and simple terminal device to today's standards. It was used by astronauts to communicate with the primary guidance computer programs. DSKY is interesting since it only had some latching relays to drive the segment displays and some simple transistor type logic to generate keycodes from the keyboard.

Today (2017) this device would be manufactured using maybe a single micro-controller and would be very simple. I am sure that even nowadays many astronauts would like to have a similar device to communicate with the guidance computer at least as a reserve device in case of some problem with the modern touch screens and high resolution displays. Its small size, simplicity and integration with the Apollo software and hardware will keep this device popular in the future also. Most of this material is from /1/. This text and drawings /1/ did have some differences with other documents but is anyway useful in its detail.

The AGC (and DSKY) was designed at the MIT Instrumentation Laboratory under Charles Stark Draper, with hardware design led by Eldon C. Hall. Early architectural work came from J.H. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso, and Hugh Blair-Smith. The flight hardware was fabricated by Raytheon, whose Herb Thaler was also on the architectural team.

Eldon C. Hall

Most of these people can be seen in the following film

YouTube video: "Computer for Apollo, MIT Science Reporter Film"]

Extreme Points of a Great Circle - (Part 3, Great Circles)

The Northernmost and Southernmost Points of a Great Circle

If you travel from Amsterdam (P1 in Figure 1) to San Francisco (P2) or the other way around, then you first go towards the north for a while, and then towards the south for a while. All great circles except for the equator have a northernmost point (PN) and a southernmost point (PS). You can calculate them as follows.

Fig. 1: Northernmost and Southernmost Point on a Great Circle

Certain Direction from a Point - (Part 2, Great Circles)

Suppose you want to know where you go if you start from a particular town in a particular direction and keep going straight (along a great circle). You can calculate the coordinates of points along the route as follows:

Fig. 2. Mercator and Hondius

Definition of a Great Circle - (Part 1, Great Circles)

[Since great circle calculations are so important on all spheres (like Earth, planets, polar coordinates, etc.) I have to add here such a text. This follows mostly /1/]

Fig. 7. Arthur H. Robinson 1979

["Arthur H. Robinson (January 5, 1915 – October 10, 2004) was an American geographer and cartographer, who was professor in the Geography Department at the University of Wisconsin–Madison from 1947 until he retired in 1980. He was a prolific writer and influential philosopher on cartography.

One of Robinson's most notable accomplishments is the Robinson projection. In 1961, Rand McNally asked Robinson to choose a projection for use as a world map that, among other criteria, was uninterrupted,[9] had limited distortion, and was pleasing to the eye of general viewers.[10] Robinson could not find a projection that satisfied the criteria, so Rand McNally commissioned him to design one.

Robinson proceeded through an iterative process to create a pseudo-cylindrical projection that intends to strike a compromise between distortions in areas and in distances, in order to attain a more natural visualization. The projection has been widely used since its introduction. In 1988, National Geographic adopted it for their world maps but replaced it in 1998 with the Winkel tripel projection."]

Mars Atmosphere and Water

There seems to be often a discussion about the Martian atmosphere and water there. But it is not commonly understood what effects the low pressure has to water on Mars (and generally in space). Most of us have done some water chemistry in schools and it is usually known how water reacts to pressure and temperature so that it is either solid, liquid or vapor and that there exists so called triple point where all these phases meet. The following figure shows the general water phase diagram relative to the pressure and temperature.

Figure 1. Water Phase Diagram

In this diagram we can see that as the pressure gets lower we come to the triple point below which there is no more any liquid water available. In space where there is the zero pressure there is no liquid water possible, it boils instantly. Only solid and vapor is possible.

Since in any atmosphere (Earth and Mars) the pressure gets lower when we go higher it is more convenient to show this diagram inverted so that it shows the phenomena relative to the altitude. Below is such a diagram drawn for Earth or Mars.

Figure 2. Water Phase Diagram on Earth and Mars

In this diagram we can see on the left the "normal" situation on Earth (the space might be the more general situation). And we are very used to liquid water since it exists between 0 and 100 C degrees, and is the most common water phase here on Earth. But we seem to forget that Earth surface is just a small exception in the huge space.

When we move to the Mars (on the right in the diagram) we instantly notice that we have lost our liquid water since Mars mean surface pressure is almost exactly water's triple point. And that we cannot even find any liquid water if we go higher in the atmosphere since the pressure just gets lower. Also if we consider the typical low temperatures on Mars we see that any liquid water would be very rare there. Also if the typical liquid water range here on Earth is 0 to 100 C degrees, on Mars it might be just 5 C degrees in very low places and high Mars temperatures. So it is rather clear why there is no living plants possible on Mars without heated pressurized shelters.

In this diagram we can also see that the mean Mars surface is at about 35 km altitude compared to the Earth's atmosphere and we also know that nothing much usually lives naturally above 6 km here on Earth, top of the Mount Everest for example.

["There is very little native flora or fauna on Everest. There is a moss that grows at 6,480 metres (21,260 ft) on Mount Everest. It may be the highest altitude plant species. An alpine cushion plant called Arenaria is known to grow below 5,500 metres (18,000 ft) in the region"]


VIDEOS

YouTube video: "Water Boiling at Room Temperatures, Under a Vacuum"

* * *

Apollo Mission Films (Part 14, Apollo Control Systems)

NASA made several films during the Apollo program about the physics, calculations and programming principles used to do the manned Moon trip. Compared to today's standards many of those are very detailed and give very good information about how the programs behind the successful missions were tailored. Most of films originated from MSC (Manned Spacecraft Center) Houston, Texas. This is a list of links I have found in YouTube (there might be more in various archives).

1950's Computer Language "George"

[The Laning and Zierler system (sometimes called "George" by its users) was one of the first operating algebraic systems, that is, a system capable of accepting mathematical formulae in algebraic notation and executing equivalent machine code.

The system accepted formulas in a more or less algebraic notation. It respected the standard rules for operator precedence, allowed nested parentheses, and used superscripts to indicate exponents.

It was among the first programming systems to allow symbolic variable names and allocate storage automatically. The system also automated the following tasks: floating point computation, linkage to subroutines for the basic functions of analysis (sine, etc.) and printing, and arrays and indexing. It could also solve automatically ordinary differential equations using Gills' variation of the 4th order Runge-Kutta Method, that was an inbuilt language feature.

Dr. J. Halcombe Laning

It was implemented in 1952-53 and published in 1954 for the MIT WHIRLWIND computer by J. Halcombe Laning and Neal Zierler. It was made during a time with similar UNIVAC A-2, IBM Speedcoding and a number of other systems that were proposed but never implemented.

The following text is a reprint of a MIT's summer session report 1954.]

LM Descent to the Moon - Part 7 - Crew Comments (1969)

(Apollo 11 LM - DOI to Touchdown Crew Debriefing, 1969)

[The following is a partial reprint of NASA's Apollo 11 crew interviews /1/ during their quarantine that took three weeks after their splash down. Apollo 11 CM splashed down on July 24, 1969.]

Figure 1. ARMSTRONG, COLLINS and ALDRIN.
The Apollo 11 mission, launched on July 16, 1969 and returned to Earth on July 24, 1969. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. Aldrin Jr., Lunar Module (LM) pilot

DSKY Interface (Part 13, Apollo Control Systems)

(DSKY I/O Interface, Apollo Guidance Computer)

[This article describes how the Apollo Guidance Computer (AGC) was connected to the Display and Keyboard Unit (DSKY). This is rather detailed description about the hardware and gives some light about how various devices were connected to the AGC. Since the connection was digital and parallel no special arrangements was required as with the more sensitive analog interfaces. The text is mainly from reference /1/.]

Figure 1. DSKY (Apollo Guidance Computer Display and Keyboard)

LM Descent to the Moon - Part 6 - Programming (1971)

(Apollo Lunar-Descent Guidance, 1971)

[The following MIT / NASA's 1971 text, partial reprint of the reference /0/, describes the descent algorithms used in the Apollo Lunar Module computer program (Luminary version 099/1A, about 63,000 lines of YUL assembly code) and flown summer 1969. This paper actually describes an advanced version of the algorithm which was not used since the older version which was more tested at that time (1969) was good enough for the job. What so ever, the text gives a good glance to the manned planetary descent programming.]

Figure 1. Components of the Lunar-Descent Guidance System.

(Mars) Vehicle "2500" - Part 2 - The Plans

Basically if the target planet or object has less gravity than Mars and/or any atmosphere or not at all like Earth's Moon this vehicle should be fine. It differs from the Apollo Lunar Module in those parts which require aerodynamics but is otherwise similar. It can be used with some amount of AB (aero braking) but it can also handle braking with rockets alone. If much gas is available for braking then less fuel is required and that mass can be used for transport purposes if required. So basically our design is a general purpose lander, but fits best to Mars, Moons etc.

Here is the more detailed general plan of the vehicle "2500".

Figure 1. General purpose lander for Mars, Moons, etc.

Mars Vehicle "2500" - Part 1 - Basics

This Mars Vehicle (MV), model "2500" is part of the LEAMOR (Light Extended Apollo Mars Orbit Rendezvous) total mission plan. See the article for general ideas about that Mars mission plan.

Figure 1. Mars Vehicle (MV) "2500" with ablative lower part and heat shield above ablative fuel balls.

LM Descent to the Moon - Part 5 - Powered Landing Maneuver (1964)

(LEM Powered Landing Maneuver, 1964)

[This is a partial reprint of a 1964 technical paper from MIT/NASA, which explains the mathematics behind the 1960's lunar landings. See /1/ for details. LM was called LEM (Lunar Excursion Module) those days and the first landing was to be done summer 1969, 5 years after this paper was written. The strength of this algorithm is that it is real time adaptive to the variations of the parameters from different sources (and also errors). This algorithm was called "E Guidance" due to the E matrix used in it. The basic LM descent guidance logic was defined by an acceleration command which was a quadratic function of time and was, therefore, later termed "Quadratic Guidance". ]

Figure 0. Look angle "lambda" is relative to the thrust axis

Command Module ECS (Part 12, Apollo Control Systems)

Environmental Control System (ECS)

The Apollo environmental control system (ECS) was designed and qualified to support three crewmen for 14 days and to maintain electronic equipment within operating thermal boundaries. The system maintains the pressure atmosphere of 100 percent oxygen and removes trace contaminants and metabolic carbon dioxide by absorption in charcoal and lithium hydroxide beds. (After the Apollo 1 CM accident the launch atmosphere was changed to 60-percent oxygen and 40-percent nitrogen.)

Apollo CM Environmental Control Unit (ECU), a major part of the ECS

[An Apollo Command Module (Block II) Environmental Control Unit (ECU) a major part of the Environmental Control subsystem (ECS), produced by Garrett Corp.'s AiResearch Division, Los Angeles under subcontract to North American Aviation (NAA), prime for the Apollo Command Service Module (CSM) under NASA Contact NAS 9-150. The Environmental Control Unit was the heart of the environmental control subsystem. It is a compact grouping of equipment about 29 inches long, 16 inches deep, and 33 inches at its widest point. It was mounted in the left-hand equipment bay. The unit contains the coolant control panel, water chiller, two water-glycol evaporators, carbon dioxide-odor absorber canisters, and suit heat exchanger, water separator, and compressors.]

CM Command Module (Part 11, Apollo Control Systems)

This article handles the Apollo Command Module. The current NASA command module is called Orion capsule or crew module.

Command Module CM with the Service Module SM connected together with an umbilical (right).  

JB-10 Latest Jetpack

Looks like Jetpack people have again created a new version of their "real jetpack", real meaning that it really uses jets and not rockets like some earlier versions of jetpacks did.

Jetpack JB-10 new in 2016 flown single handed.